Digital reception apparatus for removing distortion from received signals

ABSTRACT

A digital reception apparatus includes a receiver that processes a received signal and a distortion corrector that corrects a non-linear distortion of the processed received signal, introduced by the receiver. The receiver may include an amplifier, a quadrature demodulator and/or a quantizer. The distortion corrector includes a distortion estimator that estimates the distortion and outputs a correcting signal based on an inverse distortion characteristic of the receiver, and a distortion compensator that multiplies the received signal and the correcting signal to remove the non-linear distortion from the received signal, to obtain a corrected received signal. The corrected signal is output to a demodulator, which performs demodulation processing on the corrected signal, and thereby obtains a demodulated signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reception apparatus used in a digitalcommunication.

2. Description of the Related Art

Conventionally, in a reception apparatus used in a digital communication(hereinafter referred to as “digital reception apparatus”), on theassumption that the linearity is maintained in the reception processingon received signals, the demodulation processing has been executed onthe received signals subjected to the reception processing. When thelinearity is not maintained in the reception processing on receivedsignals, characteristics of demodulated signals deteriorate which areobtained by performing the demodulation processing on thereception-processing processed received signals.

For example, a case is assumed that in the demodulation processing onthe reception-processing processed received signals, unnecessaryfrequency signal components are divided from the reception-processingprocessed received signals to obtain only necessary frequency signalcomponents. In this case, when the linearity is not maintained in thereception processing on received signals, it is difficult to divide theunnecessary frequency signal components from the reception-processingprocessed received signals, and also, even necessary frequency signalcomponents are sometimes removed from the reception-processing processedreceived signals. The characteristics of the demodulated signalsobtained by the demodulation processing thereby deteriorate.

Accordingly, the conventional digital reception apparatus is designed tohighly maintain the linearity in the reception processing to thereceived signals.

Meanwhile, recent digital communications require communications for fasttransmitting a large amount of information. In order to satisfy such arequirement, the quadrature amplitude modulation (QAM) or the like isapplied as a modulation scheme, and/or the spread spectrum system inwhich a plurality of channels are multiplexed in a communication bandand/or the OFDM (Orthogonal Frequency Division Multiplexing) system isused as a communication system.

However, when QAM or the like is applied as a modulation scheme, and/orthe spread spectrum system and/or the OFDM system is used as acommunication system, a signal amount per communication band isincreased. Therefore, the power/amplitude of received signals isincreased, which causes a problem that it becomes very difficult tomaintain the linearity in the reception processing to the receivedsignals. As a result, the characteristics of the demodulated signalsobtained by the demodulation processing deteriorate.

Therefore, in the recent case where the communication system is appliedthat increases the signal amount per communication band, a technique hasbeen quite desired that highly maintains the linearity in the receptionprocessing in the digital reception apparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a digital receptionapparatus that maintains excellent characteristics in demodulationsignals obtained by demodulating received signals. The object isachieved by using a characteristic of a receiving section that performsreception processing on the received signals, and thereby removingnon-linear distortions from the reception-processing processed receivedsignals.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the invention will appearmore fully hereinafter from a consideration of the following descriptiontaken in connection with the accompanying drawing wherein one example isillustrated by way of example, in which;

FIG. 1 is a block diagram illustrating a configuration of a digitalreception apparatus according to a first embodiment of the presentinvention;

FIG. 2 is a block diagram illustrating a configuration of a digitalreception apparatus according to a second embodiment of the presentinvention;

FIG. 3 is a block diagram illustrating a configuration of a digitalreception apparatus according to a third embodiment of the presentinvention;

FIG. 4 is a block diagram illustrating a configuration of a digitalreception apparatus according to a fourth embodiment of the presentinvention;

FIG. 5 is a block diagram illustrating a configuration of a digitalreception apparatus according to a fifth embodiment of the presentinvention;

FIG. 6 is a block diagram illustrating a configuration of a digitalreception apparatus according to a sixth embodiment of the presentinvention;

FIG. 7 is a block diagram illustrating a configuration of a digitalreception apparatus according to a seventh embodiment of the presentinvention;

FIG. 8 is a block diagram illustrating a configuration of a digitalreception apparatus according to an eighth embodiment of the presentinvention;

FIG. 9 is a block diagram illustrating a configuration of a digitalreception apparatus according to a ninth embodiment of the presentinvention;

FIG. 10A is a schematic view showing an example of the relationshipbetween an input signal and output code in conventional linearquantization;

FIG. 10B is a schematic view showing an example of the relationshipbetween an input signal and output code in non-linear quantization inthe digital reception apparatus according to the ninth embodiment of thepresent invention;

FIG. 11A is a schematic view illustrating an example of a conversiontable for use by a non-linearly quantizing section n the digitalreception apparatus according to the ninth embodiment of the presentinvention;

FIG. 11B is a schematic view illustrating an example of a conversiontable for use by a linearly compensating section in the digitalreception apparatus according to the ninth embodiment of the presentinvention;

FIG. 12 is a block diagram illustrating a configuration of a digitalreception apparatus according to a tenth embodiment of the presentinvention;

FIG. 13 is a block diagram illustrating a configuration of a digitalreception apparatus according to an eleventh embodiment of the presentinvention;

FIG. 14 is a block diagram illustrating a configuration of a digitalreception apparatus according to a twelfth embodiment of the presentinvention;

FIG. 15 is a block diagram illustrating a configuration of a digitalreception apparatus according to a thirteenth embodiment of the presentinvention; and

FIG. 16 is a block diagram illustrating a configuration of a digitalreception apparatus according to a fourteenth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described specificallybelow with reference to accompanying drawings.

First Embodiment

In this embodiment, a case is explained that distortion correction isperformed to a received signal having a distortion due to the receptionprocessing, using the inverse characteristic of an analog element thatperforms the reception processing.

FIG. 1 is a block diagram illustrating a configuration of a digitalreception apparatus according to the first embodiment of the presentinvention. The digital reception apparatus according to this embodimentis provided with receiving section 101, amplifying section 102,distortion correcting section 103 having distortion estimating section103 a and distortion compensating section 103 b, and demodulatingsection 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained. A signal transmitted from atransmitting-side apparatus (for example, a base station apparatus andmobile station apparatus) is received, through a propagation path, inreceiving section 101 in the digital reception apparatus according tothis embodiment. A signal 150 (received signal) received in receivingsection 101 is amplified in amplifying section 102 to be an amplifiedsignal 151. When the characteristic of amplifying section 102 contains adistortion, the characteristic of the amplified signal 151 obtained inamplifying section 102 also contains a distortion.

The amplified signal 151 is output to distortion estimating section 103a and distortion compensating section 103 b in distortion correctingsection 103.

Distortion estimating section 103 a has information on the distortioncharacteristic of amplifying section 102 input beforehand thereto.Distortion estimating section 103 a estimates a distortion componentcontained in the amplified signal 151, using the information on thedistortion characteristic of amplifying section 102 and the amplifiedsignal 151 from amplifying section 102. Further, using the estimateddistortion component, the section 103 a generates a correcting signal152 to correct the distortion component of the amplified signal 151.

Distortion estimating section 103 a is comprised of, for example, anelement having the inverse characteristic of a section where theresultant signal needs the correction (in this case, amplifying section102). When such an element receives as its input the amplified signal151 from amplifying section 102, the element outputs a signal indicativeof the inverse characteristic of the amplified signal 151 as thecorrecting signal 152.

The correcting signal 152 generated in distortion estimating section 103a is output to distortion compensating section 103 b. Distortioncompensating section 103 b multiplies the amplified signal 151 fromamplifying section 102 by the correcting signal 152 from distortionestimating section 103 a. A corrected amplified signal 153 is therebyobtained which equals the amplified signal 151 from which the distortioncomponent is removed. The obtained corrected amplified signal 153 isoutput to demodulating section 104. Demodulating section 104 performsthe demodulation processing on the corrected amplified signal 153, andthereby obtains a demodulated signal 154.

The linearity in the aforementioned digital reception apparatus will beexplained next. In the case where the amplified signal 151 obtained inamplifying section 152 contains a distortion, the linearity is notmaintained in amplifying section 102. Accordingly, when demodulatingsection 104 demodulates the amplified signal obtained in amplifyingsection 102 with no correction or modification like in the conventionalmethod, the characteristic of the demodulated signal obtained indemodulating section 104 deteriorates.

However, in this embodiment, the distortion of the amplified signalobtained in amplifying section 102 is removed in distortion compensatingsection 103 b, and then the resultant signal is output to demodulatingsection 104. The linearity is thereby maintained in the receptionprocessing (for example, the amplification in amplifying section 102) tothe received signal. As a result, the characteristic of the demodulatedsignal 154 obtained in demodulating section 104 is maintained excellent.

The next description explains differences between the distortioncorrection performed by the digital reception apparatus according tothis embodiment and the equalizing technique performed by an equalizer.The equalizing technique is such a technique that removes a distortiongenerated on a propagation path from a received signal, using estimatedpropagation path characteristics.

One of the large differences between the distortion correction performedin this embodiment and the equalizing technique is that kinds of signalsto be subjected to the distortion correction are different therebetween.That is, the distortion correction is performed to a signal sequence inthe equalizing technique (specifically, the distortion correction isperformed using a previous signal sequence). In contrast thereto, thedistortion correction is performed to an instantaneous signal in thisembodiment.

Second one of the differences is whether the calculation processing foruse in actually correcting a distortion is non-linear processing orlinear processing. That is, in the equalizing technique, the distortioncorrection is performed by the calculation processing that fetchesnecessary signals from an input signal sequence based on a previoussignal sequence. In other words, the calculation processing performed incorrecting the distortion is the linear processing. In addition, as partof the signal sequence used in this calculation processing, non-linearinformation that is a judged result is used. In contrast to this, thecalculation processing performed in correcting the distortion is thenon-linear processing. That is, the compensation characteristic for theinstantaneous power differs for each instantaneous power. For example,the case where the value of an input signal is 1 and the case where thevalue is 2 will be described here. When the compensation characteristicfor an instantaneous power of each input signal is 1 and 0.7respectively, a value of an output signal for the value of the formerinput signal becomes 1, and a value of an output signal for the value ofthe latter input signal becomes 1.4.

In the foregoing, the differences between the distortion correctionperformed by the digital reception apparatus according to thisembodiment and the equalizing technique performed by an equalizer areexplained.

Amplifying section 102 has the distortion characteristic that remainsconstant with respect to the amplitude of an input signal (or outputsignal). Accordingly, by inputting in advance the distortioncharacteristic to distortion estimating section 103 a, using thedistortion characteristic, distortion estimating section 103 a is ableto estimate the distortion component in the amplified signal 151obtained in amplifying section 102. Further, distortion compensatingsection 103 b is able to remove the distortion component in theamplified signal 151 obtained in amplifying section 102. According tosuch a method, distortion correcting section 103 is able to adopt aconfiguration with one input and with one output, and therefore, it isnot necessary to change in particular a configuration of the digitalreception apparatus.

According to this embodiment, it is possible to use even an amplifyingelement having a distortion in a demodulating system requiring thelinearity. Further in the conventional method, in order to demodulatesignals at a broad band where the amplitude varies greatly whilemaintaining the linearity, it is necessary to reserve the linearity in awide range in every element composing the reception apparatus. However,according to this embodiment, it is made possible to remove a distortionreadily from a received signal by inputting in advance the distortioncharacteristics of the whole receiving configuration to distortionestimating section 103 a, whereby it is possible to make the receptionapparatus miniaturized and inexpensive.

In the conventional method, the design on the linearity of elementscomposing the reception apparatus limits a range of received signals.Accordingly, the linearity of these elements is only maintained whencharacteristics of a received signal are predicted in advance. Accordingto this embodiment, since the linearity can be maintained in asufficiently wide range, the reception apparatus is effectiveparticularly in a demodulation system that does not limit receivedsignals in particular (for example, a system with the demodulatingsection achieved by software).

In the general reception apparatus, since the linearmodulation/demodulation is basically adopted, it is preferable to use alinear amplifying element as amplifying section 102. However, all theamplifying elements have the distortion characteristic that theresultant is non-linear with respect to an input signal. The distortioncharacteristic is often caused by that output signals are saturated, andusually remains constant with respect to the instantaneous power of aninput signal. Therefore, an input signal is uniquely determined withrespect to the output signal. Accordingly, only using an output signalof amplifying section 102 (namely, amplified signal 151), distortioncorrecting section 103 is able to estimate an ideal output signal, inother words, to remove the distortion from the amplified signal 151 fromamplifying section 102.

Meanwhile, when an input signal (received signal 150) is not uniquelydetermined with respect to the output signal (amplified signal 151) ofamplifying section 102, distortion correcting section 103 outputs theinformation on some characteristic (for example, power) of the receivedsignal 150 to distortion correcting section 103 without passing theinformation through amplifying section 102, whereby it is made possibleto remove the distortion from the amplified signal 151. Further, in thiscase, if the effect is limited, it is possible to estimate an idealoutput signal from the output signal (amplified signal 151) ofamplifying section 102. However, in this case, there is a possibilitythat as a signal from which the distortion is removed, such a signal isobtained that is different from the ideal output signal.

When the distortion characteristic of amplifying section 102 is designedin advance, for example, when the distortion characteristic ofamplifying section 102 is designed by an arithmetical calculation,distortion correcting section 103 is readily configured only with theinverse characteristic of amplifying section 102 given thereto, whichfacilitates the configuration of distortion correcting section 103.Further, if it is possible to measure or design in advance thedistortion characteristic of amplifying section 102, it is possible toconfigure distortion correcting section 103 optimal for removing thedistortion characteristic, and furthermore, for example, by representinga change in the distortion characteristic of amplifying section 102 byan arithmetical calculation or storing the change in a reference table,it is possible to configure distortion correcting section 103 with highapplicability.

While this embodiment limits a distortion that distortion correctingsection 103 corrects to only a distortion generated in amplifyingsection 102, the distortion that distortion correcting section 103corrects is not limited in particular. In other words, distortioncorrecting section 103 is able to perform overall corrections includingdistortions generated in elements (analog circuits such as a filterelement and a mixer element used in frequency conversion) other thanamplifying section 102. It is thereby possible to obtain the distortioncorrection effects with higher accuracy.

As described above, in this embodiment, the distortion correction isperformed to received signals with distortions caused by the receptionprocessing, using the inverse characteristic of an analog element thatexecutes the reception processing. The linearity is thereby maintainedin the reception-processing processed received signals to be used indemodulation processing. Accordingly, the excellent characteristics aremaintained in demodulated signals obtained by demodulating thereception-processing processed received signals.

Second Embodiment

FIG. 2 is a block diagram illustrating a configuration of a digitalreception apparatus according to the second embodiment of the presentinvention. In addition, in FIG. 2, the same sections as in the firstembodiment (FIG. 1) are assigned the same reference numerals as in FIG.1, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, amplifying section 102, quadraturedemodulation section 201, distortion correcting section 202 havingdistortion estimating section 202 a and distortion compensating sections202 b and 202 c, and demodulating section 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only given to points differentfrom the first embodiment.

The amplified signal 151 is demodulated in quadrature demodulationsection 201 to be a baseband signal composed of an in-phase signal 250 band a quadrature signal 250 c. The in-phase signal 250 b (quadraturesignal 250 c) in the baseband signal is output to distortion estimatingsection 202 a and to distortion compensating section 202 b (distortioncompensating section 202 c) in distortion correcting section 202.

At this point, when the characteristic of amplifying section 102contains a distortion, the characteristic of the amplified signal 151obtained in amplifying section 102 also contains a distortion. Further,vector components of the distortion are also contained in the in-phasesignal 205 b and quadrature signal 205 c in the baseband signal.

Distortion estimating section 202 a has information on the vectorcomponents of the distortion characteristic of amplifying section 102input beforehand thereto. Distortion estimating section 202 a estimatesthe distortion components respectively contained in the in-phase signal250 b and quadrature signal 250 c in the baseband signal obtained inquadrature demodulation section 201, using the information on thedistortion characteristic of amplifying section 102, and the in-phasesignal 250 b and quadrature signal 250 c in the baseband signal.Further, using the estimated distortion component, the section 202 agenerates a correcting signal 251 b (correcting signal 251 c) to correctthe distortion component of the in-phase signal 250 b (quadrature signal250 c) in the baseband signal.

Distortion estimating section 202 a is comprised of, for example, anelement having the inverse characteristic of a section where theresultant signal needs the correction (in this case, amplifying section102). Generally, vector represented components of the distortioncharacteristic of amplifying section 102 are not lost and contained inthe baseband signal obtained in quadrature demodulation section 201.Accordingly, when such an element receives as its input the in-phasesignal 250 b (quadrature signal 250 c) in the baseband signal fromquadrature demodulation section 201, the element outputs a signalindicative of the inverse characteristic concerning on a distortioncontained in the in-phase signal 250 b (quadrature signal 250 c) in thebaseband signal as the correcting signal 251 b (correcting signal 251c). In addition, that the distortion characteristic of amplifyingsection 102 is represented by vectors is, in detail, equal to that thedistortion is represented by vectors with an amplitude component and aphase component.

The correcting signal 251 b (correcting signal 251 c) generated indistortion estimating section 202 a is output to distortion compensatingsection 202 b (distortion compensating section 202 c). Distortioncompensating section 202 b (distortion compensating section 202 c)multiplies the in-phase signal 250 b (quadrature signal 250 c) fromquadrature demodulation section 201 by the correcting signal 251 b(correcting signal 251 c) from distortion estimating section 202 a. Acorrected amplified signal 252 b (corrected amplified signal 252 c) isthereby obtained which equals the in-phase signal 250 b (quadraturesignal 250 c) from which the distortion component is removed.

The obtained corrected amplified signals 252 b and 252 c are output todemodulating section 104. Demodulating section 104 performs thedemodulation processing on the corrected amplified signals 252 b and 252c, and thereby obtains a demodulated signal 252.

Amplifying section 102 has the distortion characteristic that remainsconstant with respect to the amplitude of an input signal (or outputsignal). Further, components of the distortion characteristicrepresented by vectors are not lost after being subjected to thequadrature demodulation. Accordingly, by inputting in advance thedistortion characteristic as vector values to distortion estimatingsection 202 a, using the distortion characteristic, distortionestimating section 202 a is able to estimate the distortion component inthe amplified signal 151 obtained in amplifying section 102 (i.e., thedistortion component in the baseband signal obtained in quadraturedemodulation section 201). Further, distortion compensating section 202b (distortion compensating section 202 c) is able to remove thedistortion component in the in-phase signal 250 b (quadrature signal 250c).

According to such a method, since the distortion characteristic ofamplifying section 102 is represented by vectors, distortion correctingsection 202 is able to correct the amplitude distortion and phasedistortion in the baseband signal obtained in quadrature demodulationsection 201. It is thereby possible to reserve the particularly highlinearity in the corrected amplified signals 252 b and 252 c with thedistortion corrected in distortion correcting section 202.

According to this embodiment, it is possible to use even an amplifyingelement having a distortion in a demodulating system requiring thelinearity. Further in the conventional method, in order to demodulatesignals at a broad band where the amplitude varies greatly whilemaintaining the linearity, it is necessary to reserve the linearity in awide range in every element composing the reception apparatus. However,according to this embodiment, by inputting in advance the distortioncharacteristics of the whole receiving configuration to distortionestimating section 202 a, it is made possible to remove a distortionreadily from a received signal, and a range of the amplitude ofmanageable signals expands, whereby it is possible to make the receptionapparatus miniaturized and inexpensive.

In the conventional method, the design on the linearity of elementscomposing the reception apparatus limits a range of received signals.Accordingly, the linearity of these elements is only maintained whencharacteristics of a received signal are predicted in advance. Accordingto this embodiment, since the linearity can be maintained in asufficiently wide range, the reception apparatus is effectiveparticularly in a demodulation system that does not limit receivedsignals in particular (for example, a system with the demodulatingsection achieved by software).

In the general reception apparatus, since the linearmodulation/demodulation is basically adopted, it is preferable to use alinear amplifying element as amplifying section 102. However, all theamplifying elements have the distortion characteristic that theresultant is non-linear with respect to an input signal. The distortioncharacteristic is often caused by that output signals are saturated, andusually remains constant with respect to the instantaneous power of aninput signal. Therefore, an input signal is uniquely determined withrespect to the output signal. Accordingly, only using an output signalof quadrature demodulation section 201 (namely, the in-phase signal 250b and quadrature signal 250 c in the baseband signal), distortioncorrecting section 202 is able to estimate an ideal output signal, inother words, to remove the distortion from the baseband signal fromquadrature demodulation section 201.

Meanwhile, when an input signal (received signal 150) is not uniquelydetermined with respect to the output signal (amplified signal 151) ofamplifying section 102, distortion correcting section 202 outputs theinformation on some characteristic (for example, power) of the receivedsignal 150 to distortion correcting section 202 without passing theinformation through amplifying section 102, whereby it is made possibleto remove the distortion from the amplified signal 151.

Further, in this case, if the effect is limited, it is possible toestimate an ideal output signal from the output signal (amplified signal151) of amplifying section 102. However, in this case, there is apossibility that as a signal from which the distortion is removed, sucha signal is obtained that is different from the ideal output signal.

When the distortion characteristic of amplifying section 102 is designedin advance, for example, when the distortion characteristic ofamplifying section 102 is designed by an arithmetical calculation,distortion correcting section 202 is readily configured only with theinverse characteristic of amplifying section 102 given thereto, whichfacilitates the configuration of distortion correcting section 202.Further, if it is possible to measure or design in advance thedistortion characteristic of amplifying section 102, it is possible toconfigure distortion correcting section 202 optimal for removing thedistortion characteristic, and furthermore, for example, by representinga change in the distortion characteristic of amplifying section 102 byan arithmetical calculation or storing the change in a reference table,it is possible to configure distortion correcting section 202 with highapplicability.

While this embodiment limits a distortion that distortion correctingsection 202 corrects to only a distortion generated in amplifyingsection 102, the distortion that distortion correcting section 202corrects is not limited in particular. In other words, distortioncorrecting section 202 is able to perform overall corrections includingdistortions generated in elements (analog circuits such as a filterelement and a mixer element used in frequency conversion) other thanamplifying section 102. It is thereby possible to obtain the distortioncorrection effects with higher accuracy.

As described above, in this embodiment, the distortion correction isperformed to received signals with distortions caused by the receptionprocessing, using the inverse characteristic of an analog element thatexecutes the reception processing. The linearity is thereby maintainedin the reception-processing processed received signals to be used indemodulation processing. Accordingly, the excellent characteristics aremaintained in demodulated signals obtained by demodulating thereception-processing processed received signals. Further, in thisembodiment, since the distortion correction is performed to the basebandsignal obtained by the quadrature demodulation, it is possible to removeboth the amplitude distortion and phase distortion in the receivedsignals to be input to the demodulating section.

Third Embodiment

FIG. 3 is a block diagram illustrating a configuration of a digitalreception apparatus according to the third embodiment of the presentinvention. In addition, in FIG. 3, the same sections as in the firstembodiment (FIG. 1) are assigned the same reference numerals as in FIG.1, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, filtering section 301, quantizing section302, distortion correcting section 303, and demodulating section 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only given to points differentfrom the first embodiment.

The received signal 150 from receiving section 101 is subjected the bandlimitation in filtering section 301 which cancels refrain errors and soon. A band limited signal 350 is thereby obtained. The obtained bandlimited signal 350 is output to quantizing section 302.

Quantizing section 302 performs quantization (i.e., non-linearquantization) on the band limited signal 350, while changing aquantization step corresponding to the amplitude of the band limitedsignal 350 input thereto. A non-linear quantized signal 351 is therebyobtained. In addition, the non-linear quantization will be describedspecifically later. The obtained non-linear quantized signal 351 isoutput to distortion correcting section 303.

Distortion correcting section 303 has information on the relationshipbetween an input signal and output signal in quantizating section 303input beforehand thereto. Using the information, distortion correctingsection 303 linearizes the non-linear quantized signal 351. A correctedquantized signal 352 is thereby obtained. The obtained correctedquantized signal 352 is demodulated in demodulating section 104. Ademodulated signal 353 is thereby obtained.

In the conventional quantization, the whole range of the amplitudeavailable for received signals to be quantized is divided into aplurality of quantization steps each with a constant signal width, andeach quantization step is assigned a code specific to the quantizationstep. This processing equals dispersing a quantization error over allthe signals with equal levels. Then, the whole range of the amplitudeavailable for received signals to be quantized is divided into aplurality of quantization steps with mutually different signal widths,and each quantization step is subjected to demodulation specific to thequantization step, whereby the quantization error changes, and therebycan be adjusted corresponding to the amplitude of the signal.

Using the above processing enables the adjustment of a noise to beprovided to the digital reception apparatus. The receptioncharacteristics of the digital reception apparatus are determined by asystem noise represented by noise index, quantization error, calculationerror, etc. The system noise remains almost constant regardless ofreceived level, and the effect of the calculation error tends todecrease as the amplitude of a signal to be processed increases.

Therefore, for example, by making the sum of the quantization error andcalculation error constant, or by sacrificing the characteristic at ahigh C/N environment, it is possible to increase the quantization erroras the amplitude of a signal increases. Specifically, the quantizingsection assigns a quantization step with a small signal width to areceived signal with the small amplitude, while assigning a quantizationstep with a large signal width to a received signal with the largeamplitude. The quantization noise caused by the quantization error isthereby weighted largely on the received signal with the largeamplitude, whereby it is possible to make the sum of the quantizationerror and calculation error constant.

Using such non-linear quantization, it is possible to expand the wholerange of the amplitude of received signals to be quantized withoutincreasing the quantization number (resolution). Further, by adjustingquantization steps to be optimal, it is possible to achieve thequantization with the small quantization number. In particular, bydesigning the quantization steps corresponding to a modulation schemeused in communications and an expected reception environment, it ispossible to design a digital reception apparatus that performs highlyefficient reception.

According to this embodiment, it is possible to use even an amplifyingelement having a distortion in a demodulating system requiring thelinearity. Further in the conventional method, in order to demodulatesignals at a broad band where the amplitude varies greatly whilemaintaining the linearity, it is necessary to reserve the linearity in awide range in every element composing the reception apparatus. However,according to this embodiment, it is made possible to remove a distortionreadily from a received signal by inputting in advance the distortioncharacteristics of the whole receiving configuration to distortionestimating section 303, whereby it is possible to make the receptionapparatus miniaturized and inexpensive.

In the conventional method, the design on the linearity of elementscomposing the reception apparatus limits a range of received signals.Accordingly, the linearity of these elements is only maintained whencharacteristics of a received signal are predicted in advance. Accordingto this embodiment, since the linearity can be maintained in asufficiently wide range, the reception apparatus is effectiveparticularly in a demodulation system that does not limit receivedsignals in particular (for example, a system with the demodulatingsection achieved by software).

In the general reception apparatus, since the linearmodulation/demodulation is basically adopted, it is preferable to use alinear amplifying element as amplifying section 102. However, all theamplifying elements have the distortion characteristic that theresultant is non-linear with respect to an input signal. The distortioncharacteristic is often caused by that output signals are saturated, andusually remains constant with respect to the instantaneous power of aninput signal. Therefore, an input signal is uniquely determined withrespect to the output signal. Distortion correcting section 303 is ableto estimate an ideal output signal with the distortion component of eachelement removed, as well as correcting the non-linearity caused by thenon-linear quantization in quantizing section 302.

When the distortion characteristic of quantizing section 302 is designedin advance, for example, when the distortion characteristic ofquantizing section 302 is designed by an arithmetical calculation,distortion correcting section 303 is readily configured only with theinverse characteristic of quantizing section 302 given thereto, whichfacilitates the configuration of distortion correcting section 303.Further, if it is possible to measure or design in advance thedistortion characteristic of quantizing section 302, it is possible toconfigure distortion correcting section 303 optimal for removing thedistortion characteristic, and furthermore, for example, by representinga change in the distortion characteristic of quantizing section 302 byan arithmetical calculation or storing the change in a reference table,it is possible to configure distortion correcting section 303 with highapplicability.

The configuration of quantizing section 302 is not limited to theabove-mentioned configuration. Quantizing section 302 may be configuredby, for example, making intervals of reference power non-equal intervalsin a quantizer having a combination of a plurality of power comparatorsand the reference power.

Further, quantizing section 302 may be configured by, for example,changing a configuration of a digital filter corresponding to theamplitude in a quantizer having a power comparator and reference power,some integrators and differentiaters, and the digital filter. In thiscase, since it is possible to achieve the integrators, differentiaters,digital filter and the like by the software (computer program), thedigital filter according to this embodiment may be achieved furtherreadily.

Distortion correcting section 303 handles quantization information, andtherefore is capable of being composed of a conventional logicalcircuit, or of being achieved by the software (computer program).

Fourth Embodiment

FIG. 4 is a block diagram illustrating a configuration of a digitalreception apparatus according to the fourth embodiment of the presentinvention. In addition, in FIG. 4, the same sections as in the secondembodiment (FIG. 2) are assigned the same reference numerals as in FIG.2, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, amplifying section 102, quadraturedemodulation section 201, quantizing section 401, distortion correctingsection 202 having distortion estimating section 202 a and distortioncompensating sections 202 b and 202 c, and demodulating section 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only given to points differentfrom the second embodiment.

The in-phase signal 250 b and quadrature signal 250 c in the basebandsignal obtained in quadrature demodulation section 201 are quantized inquantizing section 401. A quantized baseband signal containing anin-phase signal 450 b and quadrature signal 450 c is thereby generated.The generated in-phase signal 450 b (quadrature signal 450 c) in thequantized baseband signal is output to distortion estimating section 202a and to distortion compensating section 202 b (distortion compensatingsection 202 c).

At this point, when the characteristic of amplifying section 102contains a distortion, the characteristic of the amplified signal 151obtained in amplifying section 102 also contains a distortion. Further,vector components of the distortion are also contained in the in-phasesignal 250 b and quadrature signal 250 c in the baseband signal.

Distortion estimating section 202 a has information on the vectorcomponents of the distortion characteristic of amplifying section 102input beforehand thereto. Distortion estimating section 202 a estimatesthe distortion components respectively contained in the in-phase signal450 b and quadrature signal 450 c in the quantized baseband signalobtained in quantizing section 401, using the information on thedistortion characteristic of amplifying section 102, and the in-phasesignal 450 b and quadrature signal 450 c in the quantized basebandsignal. Further, using the estimated distortion component, the section202 a generates a correcting signal 451 b (correcting signal 451 c) tocorrect the distortion component of the in-phase signal 450 b(quadrature signal 451 c) in the quantized baseband signal.

The correcting signal 451 b (correcting signal 451 c) generated indistortion estimating section 202 a is output to distortion compensatingsection 202 b (distortion compensating section 202 c). Distortioncompensating section 202 b (distortion compensating section 202 c)multiplies the in-phase signal 450 b (quadrature signal 450 c) fromquantizing section 401 by the correcting signal 451 b (correcting signal451 c) from distortion estimating section 202 a. An in-phase signal 452b (quadrature signal 452 c) as a corrected baseband signal is therebyobtained which equals the in-phase signal 450 b (quadrature signal 450c) from which the distortion component is removed.

The obtained in-phase signal 452 b and quadrature signal 452 c in thecorrected baseband signal are output to demodulating section 104.Demodulating section 104 performs the demodulation processing on thein-phase 452 b and quadrature signal 452 c in the corrected basebandsignal, and thereby obtains a demodulated signal 453.

Amplifying section 102 has the distortion characteristic that remainsconstant with respect to the amplitude of an input signal (or outputsignal). Further, components of the distortion characteristicrepresented by vectors are not lost after being subjected to thequadrature demodulation. Accordingly, by inputting in advance thedistortion characteristic as vector values to distortion estimatingsection 202 a, using the distortion characteristic, distortionestimating section 202 a is able to estimate the distortion component inthe amplified signal 151 obtained in amplifying section 102 (i.e., thedistortion component in the baseband signal obtained in quadraturedemodulation section 201). Further, distortion compensating section 202b (distortion compensating section 202 c) is able to remove thedistortion component in the in-phase signal 450 b (quadrature signal 450c).

According to such a method, since the distortion characteristic ofamplifying section 102 is represented by vectors, distortion correctingsection 202 is able to correct the amplitude distortion and phasedistortion in the baseband signal obtained in quadrature demodulationsection 201. It is thereby possible to reserve the particularly highlinearity in the corrected amplified signals 452 b and 452 c with thedistortion corrected in distortion correcting section 202.

According to this embodiment, it is possible to use even an amplifyingelement having a distortion in a demodulating system requiring thelinearity. Further in the conventional method, in order to demodulatesignals at a broad band where the amplitude varies greatly whilemaintaining the linearity, it is necessary to reserve the linearity in awide range in every element composing the reception apparatus. However,according to this embodiment, by inputting in advance the distortioncharacteristics of the whole receiving configuration to distortionestimating section 202 a, it is made possible to remove a distortionreadily from a received signal, whereby it is possible to make thereception apparatus miniaturized and inexpensive.

When a signal with large power transmitted on an adjacent channel isinput as an interfering signal to the digital reception apparatusaccording to this embodiment, it is necessary to set a range ofquantization in quantizing section 401 to be large. However, under thecondition that the resolution is the same in the quantization, thequantization errors are increased, and the characteristic of ademodulated signal deteriorates. Then, it is possible to provide adistortion characteristic for limiting the amplitude to the amplifiedsignal 151 in amplifying section 102 disposed at a first part, and toperform the distortion correction corresponding to the distortioncharacteristic in distortion correcting section 202 disposed at a latterpart. It is thereby possible to provide a weight of the quantizationerror from a signal with low power to a signal with high power, andtherefore even under the condition of the same quantization resolution,the characteristic of a demodulated signal does not deteriorate inparticular.

In the conventional method, the design on the linearity of elementscomposing the reception apparatus limits a range of received signals.Accordingly, the linearity of these elements is only maintained whencharacteristics of a received signal are predicted in advance. Accordingto this embodiment, since the linearity can be maintained in asufficiently wide range, the reception apparatus is effectiveparticularly in a demodulation system that does not limit receivedsignals in particular (for example, a system with the demodulatingsection achieved by software).

In the general reception apparatus, since the linearmodulation/demodulation is basically adopted, it is preferable to use alinear amplifying element as amplifying section 102. However, all theamplifying elements have the distortion characteristic that theresultant is non-linear with respect to an input signal. The distortioncharacteristic is often caused by that output signals are saturated, andusually remains constant with respect to the instantaneous power of aninput signal. Therefore, an input signal is uniquely determined withrespect to the output signal. Accordingly, only using an output signalof amplifying section 102 (i.e., the amplified signal 151), distortioncorrecting section 202 is able to estimate an ideal output signal, inother words, to remove the distortion from the amplified signal 151 fromamplifying section 102.

Meanwhile, when an input signal (received signal 150) is not uniquelydetermined with respect to the output signal (amplified signal 151) ofamplifying section 102, distortion correcting section 202 outputs theinformation on some characteristic (for example, power) of the receivedsignal 150 to distortion correcting section 202 without passing theinformation through amplifying section 102, whereby it is made possibleto remove the distortion from the amplified signal 151. Further, in thiscase, if the effect is limited, it is possible to estimate an idealoutput signal from the output signal (amplified signal 151) ofamplifying section 102. However, in this case, there is a possibilitythat as a signal from which the distortion is removed, such a signal isobtained that is different from the ideal output signal.

When the distortion characteristic of amplifying section 102 is designedin advance, for example, when the distortion characteristic ofamplifying section 102 is designed by an arithmetical calculation,distortion correcting section 202 is readily configured only with theinverse characteristic of amplifying section 102 given thereto, whichfacilitates the configuration of distortion correcting section 202.Further, if it is possible to measure or design in advance thedistortion characteristic of amplifying section 102, it is possible toconfigure distortion correcting section 202 optimal for removing thedistortion characteristic, and furthermore, for example, by representinga change in the distortion characteristic of amplifying section 102 byan arithmetical calculation or storing the change in a reference table,it is possible to configure distortion correcting section 202 with highapplicability.

While this embodiment limits a distortion that distortion correctingsection 202 corrects to only a distortion generated in amplifyingsection 102, the distortion that distortion correcting section 202corrects is not limited in particular. In other words, distortioncorrecting section 202 is able to perform overall corrections includingdistortions generated in elements (analog circuits such as a filterelement and a mixer element used in frequency conversion) other thanamplifying section 102. It is thereby possible to obtain the distortioncorrection effects with higher accuracy.

While in this embodiment, amplifying section 102 and quantizing section401 are provided as independent elements, it may be possible toalternate the position of amplifying section 102 and that of quadraturedemodulation section 201 to provide amplifying section 102 as an inputamplifier for quantizing section 401. In this case, a non-linearquantizing element may be composed of amplifying section 102 andquantizing section 401.

Distortion correcting section 202 handles a quantized baseband signalfrom quantizing section 401, i.e., handles quantization information.Accordingly, distortion correcting section 203 is capable of beingcomposed of a conventional logical circuit, or of being achieved by thesoftware (computer program).

As described above, in this embodiment, the distortion correction isperformed to received signals with distortions caused by the receptionprocessing, using the inverse characteristic of an analog element thatexecutes the reception processing. The linearity is thereby maintainedin the reception-processing processed received signals to be used indemodulation processing. Accordingly, the excellent characteristics aremaintained in demodulated signals obtained by demodulating thereception-processing processed received signals. Further, in thisembodiment, since the distortion correction is performed to the basebandsignal obtained by the quadrature demodulation, it is possible to removeboth the amplitude distortion and phase distortion in the receivedsignals to be input to the demodulating section. In addition to theforegoing, in this embodiment, received signals with distortions causedby the reception processing are converted into digital signals, and thedistortion correction is performed to the digital received signals. Inother words, the received signals are processed as digital signals whenthe distortion correction is performed thereto. The digital receptionapparatus according to this embodiment is thereby capable of obtainingthe characteristics with high accuracy and with stability.

Fifth Embodiment

FIG. 5 is a block diagram illustrating a configuration of a digitalreception apparatus according to the fifth embodiment of the presentinvention. In addition, in FIG. 5, the same sections as in the fourthembodiment (FIG. 4) are assigned the same reference numerals as in FIG.4, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, amplifying section 102, quadraturedemodulation section 201, quantizing section 401, distortion correctingsection 202 having distortion estimating section 202 a and distortioncompensating sections 202 b and 202 c, filtering section 501, anddemodulating section 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only given to points differentfrom the fourth embodiment.

Filtering section 501 limits the frequency band of the in-phase signal452 b (quadrature signal 452 c) in the corrected baseband signal. Anin-phase signal 550 b (quadrature signal 550 c) in a band limitedbaseband signal is thereby obtained. Generally, frequencies adjacent tothe frequency used in communications by the digital reception apparatusare used in communications by other communication apparatuses.Accordingly, there is a possibility that received signals of the digitalreception apparatus contain signals transmitted from the aforementionedother communication apparatuses. However, the band limitation performedby filtering section 501 suppresses adverse effects by theaforementioned other communication apparatuses in the band limitedbaseband signals.

Demodulating section 104 demodulates the obtained in-phase signal 550 band quadrature signal 550 c in the band limited baseband signal. Therebya demodulated signal 551 is obtained.

Amplifying section 102 has the distortion characteristic that remainsconstant with respect to the amplitude of an input signal (or outputsignal). Further, components of the distortion characteristicrepresented by vectors are not lost after being subjected to thequadrature demodulation. Accordingly, by inputting in advance thedistortion characteristic as vector values to distortion estimatingsection 202 a, using the distortion characteristic, distortionestimating section 202 a is able to estimate the distortion component inthe amplified signal 151 obtained in amplifying section 102 (i.e., thedistortion component in the baseband signal obtained in quadraturedemodulation section 201). Further, distortion compensating section 202b (distortion compensating section 202 c) is able to remove thedistortion component in the in-phase signal 250 b (quadrature signal 250c).

According to such a method, since the distortion characteristic ofamplifying section 102 is represented by vectors, distortion correctingsection 202 is able to correct the amplitude distortion and phasedistortion in the baseband signal obtained in quadrature demodulationsection 201. It is thereby possible to reserve the particularly highlinearity in the corrected amplified signals, namely, the in-phasesignal 452 b and quadrature signal 452 c, with the distortion correctedin distortion correcting section 202.

According to this embodiment, it is possible to use even an amplifyingelement having a distortion in a demodulating system requiring thelinearity. In particular, under the condition that a distortion isgenerated in an analog element, it is impossible to expect the effectsas designed to an element such as a filter for performing processing ona frequency axis. Accordingly, even using the filter, it is sometimesimpossible to prevent the occurrence of an adverse effect such that partof power of information leaks into an adjacent frequency. Therefore,performing the distortion correction as explained in this embodiment hasa great effect.

For example, in a communication system where a signal band is broadwhile a plurality of channels is adjacent, it is necessary to selectonly a desired frequency signal component to extract. Achieving thisprocessing by a filter comprised of analog elements is extremelydifficult in terms of scale and accuracy.

Accordingly, in the convention system, a method is adopted where afilter for selecting a channel is comprised of a digital device.However, the filter comprised of a digital device needs to handle alsounnecessary frequency signal components until an analog signal isconverted into a digital signal. The problem thereby arises that interms of the frequency and dynamic range of the amplitude, the linearityshould be reserved by the analog element.

According to this embodiment, it is made possible to remove a distortionreadily from a received signal by inputting in advance the distortioncharacteristics of the whole receiving configuration to distortionestimating section 202 a, whereby it is possible to make the receptionapparatus miniaturized and inexpensive.

In the conventional method, the design on the linearity of elementscomposing the reception apparatus limits a range of received signals.Accordingly, the linearity of these elements is only maintained whencharacteristics of a received signal are predicted in advance. Accordingto this embodiment, since the linearity can be maintained in asufficiently wide range, the reception apparatus is effectiveparticularly in a demodulation system that does not limit receivedsignals in particular (for example, a system with the demodulatingsection achieved by software).

In the general reception apparatus, since the linearmodulation/demodulation is basically adopted, it is preferable to use alinear amplifying element as amplifying section 102. However, all theamplifying elements have the distortion characteristic that theresultant is non-linear with respect to an input signal. The distortioncharacteristic is often caused by that output signals are saturated, andusually remains constant with respect to the instantaneous power of aninput signal. Therefore, an input signal is uniquely determined withrespect to the output signal. Accordingly, only using an output signalof amplifying section 102 (namely, the amplified signal 151), distortioncorrecting section 202 is able to estimate an ideal output signal, inother words, to remove the distortion from the amplified signal 151 fromamplifying section 102.

Meanwhile, when an input signal (received signal 150) is not uniquelydetermined with respect to the output signal of amplifying section 102(amplified signal 151), distortion correcting section 202 outputs theinformation on some characteristic (for example, power) of the receivedsignal 150 to distortion correcting section 103 without passing theinformation through amplifying section 102, whereby it is made possibleto remove the distortion from the amplified signal 151. Further, in thiscase, if the effect is limited, it is possible to estimate an idealoutput signal from the output signal (amplified signal 151) ofamplifying section 102. However, in this case, there is a possibilitythat as a signal from which the distortion is removed, such a signal isobtained that is different from the ideal output signal.

When the distortion characteristic of amplifying section 102 is designedin advance, for example, when the distortion characteristic ofamplifying section 102 is designed by an arithmetical calculation,distortion correcting section 202 is readily configured only with theinverse characteristic of amplifying section 102 given thereto, whichfacilitates the configuration of distortion correcting section 202.Further, if it is possible to measure or design in advance thedistortion characteristic of amplifying section 102, it is possible toconfigure distortion correcting section 202 optimal for removing thedistortion characteristic, and furthermore, for example, by representinga change in the distortion characteristic of amplifying section 102 byan arithmetical calculation or storing the change in a reference table,it is possible to configure distortion correcting section 202 with highapplicability.

While this embodiment limits a distortion that distortion correctingsection 202 corrects to only a distortion generated in amplifyingsection 102, the distortion that distortion correcting section 202corrects is not limited in particular. In other words, distortioncorrecting section 202 is able to perform overall corrections includingdistortions generated in elements (analog circuits such as a filterelement and a mixer element used in frequency conversion) other thanamplifying section 102. It is thereby possible to obtain the distortioncorrection effects with higher accuracy.

While in this embodiment, amplifying section 102 and quantizing section401 are provided as independent elements, it may be possible toalternate the position of amplifying section 102 and that of quadraturedemodulation section 201 to provide amplifying section 102 as an inputamplifier for quantizing section 401. In this case, a non-linearquantizing element may be composed of amplifying section 102 andquantizing section 401.

Distortion correcting section 202 handles a quantized baseband signalfrom quantizing section 401, i.e., handles quantization information.Accordingly, distortion correcting section 202 is capable of beingcomposed of a conventional logical circuit, or of being achieved by thesoftware (computer program).

As described above, in this embodiment, the distortion correction isperformed to received signals with distortions caused by receptionprocessing, using the inverse characteristic of an analog element thatexecutes the reception processing. The linearity is thereby maintainedin the reception-processing processed received signals to be used indemodulation processing. Accordingly, the excellent characteristics aremaintained in demodulated signals obtained by demodulating thereception-processing processed received signals. Further, in thisembodiment, since the distortion correction is performed to the basebandsignal obtained by the quadrature demodulation, it is possible to removeboth the amplitude distortion and phase distortion in the receivedsignals to be input to the demodulating section. In addition to theforegoing, in this embodiment, received signals with distortions causedby the reception processing are converted into digital signals, and thedistortion correction is performed to the digital received signals. Inother words, the received signals are processed as digital signals whenthe distortion correction is performed thereto. The digital receptionapparatus according to the present invention is thereby capable ofobtaining the characteristics with high accuracy and with stability.

Sixth Embodiment

FIG. 6 is a block diagram illustrating a configuration of a digitalreception apparatus according to the sixth embodiment of the presentinvention. In addition, in FIG. 6, the same sections as in the thirdembodiment (FIG. 3) are assigned the same reference numerals as in FIG.3, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, filtering section 301, quadraturedemodulation section 601, quantizing section 602, distortion correctingsection 603, filtering section 604, and demodulating section 605.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only given to points differentfrom the third embodiment.

The band limited signal 350 obtained in filtering section 301 isdemodulated in quadrature demodulation section 601 to be a basebandsignal including an in-phase signal 650 a and quadrature signal 650 b.The obtained in-phase signal 650 a and quadrature signal 650 b in thebaseband signal are output to quantizing section 602.

Quantizing section 602 performs quantization (i.e., non-linearquantization) on the in-phase signal 650 a (quadrature signal 650 b) inthe baseband signal, while changing a quantization step corresponding tothe amplitude of in-phase signal 650 a (quadrature signal 650 b) in thebaseband signal input thereto. An in-phase signal 651 a (quadraturesignal 651 b) in a non-linear quantized signal is thereby obtained. Inaddition, the non-linear quantization will be described specificallylater. The obtained in-phase signal 651 a (quadrature signal 651 b) inthe non-linear quantized signal is output to distortion correctingsection 603.

Distortion correcting section 603 has information on the relationshipbetween an input signal and output signal in quantizating section 602input beforehand thereto. Using the information, distortion correctingsection 603 linearizes the in-phase signal 651 a and quadrature signal651 b in the non-linear quantized signal. An in-phase signal 652 a andquadrature signal 652 b in a corrected baseband signal are therebyobtained. Filtering section 604 limits the frequency bands of theobtained in-phase signal 652 a and quadrature signal 652 b in thecorrected baseband signal. An in-phase signal 653 a and quadraturesignal 653 b in a band limited baseband signal are thereby obtained. Theobtained in-phase signal 653 a and quadrature signal 653 b in the bandlimited baseband signal are demodulated in demodulating section 605. Ademodulated signal 654 is thereby obtained.

Quantizing section 602 has the distortion characteristic that remainsconstant with respect to the amplitude of an input signal (or outputsignal). By inputting in advance the distortion characteristic todistortion correcting section 603, using the distortion characteristic,distortion correcting section 603 is able to linearize the non-linearquantized signal obtained in quantizing section 602. Further, thenon-linear quantized signal is processed as a digital signal when thedistortion correction is performed thereto. The digital receptionapparatus according to this embodiment is thereby capable of obtainingthe characteristics with high accuracy and with stability.

In the conventional quantization, the whole range of the amplitudeavailable for received signals to be quantized is divided into aplurality of quantization steps each with a constant signal width, andeach quantization step is assigned a code specific to the quantizationstep. This processing equals dispersing a quantization error over allthe signals with equal levels. Then, the whole range of the amplitudeavailable for received signals to be quantized is divided into aplurality of quantization steps with mutually different signal widths,and each quantization step is subjected to demodulation specific to thequantization step, whereby the quantization error changes, and therebycan be adjusted corresponding to the amplitude of the signal.

Using the above processing enables the adjustment of a noise to beprovided to the digital reception apparatus. The receptioncharacteristics of the digital reception apparatus are determined by asystem noise represented by noise index, quantization error, calculationerror, etc. The system noise remains almost constant regardless ofreceived level, and the effect of the calculation error tends todecrease as the amplitude of a signal to be processed increases.

Therefore, for example, by making the sum of the quantization error andcalculation error constant, or by sacrificing the characteristic at ahigh C/N environment, it is possible to increase the quantization erroras the amplitude of a signal increases. Specifically, the quantizingsection assigns a quantization step with a small signal width to areceived signal with the small amplitude, while assigning a quantizationstep with a large signal width to a received signal with the largeamplitude. The quantization noise caused by the quantization error isthereby weighted largely on the received signal with the largeamplitude, whereby it is possible to make the sum of the quantizationerror and calculation error constant.

Using such non-linear quantization, it is possible to expand the wholerange of the amplitude of received signals to be quantized withoutincreasing the quantization number (resolution). Further, by adjustingquantization steps to be optimal, it is possible to achieve thequantization with the small quantization number. In particular, bydesigning the quantization steps corresponding to a modulation schemeused in communications and an expected reception environment, it ispossible to design a digital reception apparatus that performs highlyefficient reception.

Further, distortion correcting section 603 performs the processing usingthe vector calculation, whereby it is possible to correct the amplitudedistortion and phase distortion generated in receiving section 101.

According to this embodiment, it is possible to use even an amplifyingelement having a distortion in a demodulating system requiring thelinearity. In particular, under the condition that a distortion isgenerated in an analog element, it is impossible to expect the effectsas designed to an element such as a filter for performing processing ona frequency axis. Accordingly, even using the filter, it is sometimesimpossible to prevent the occurrence of an adverse effect such that partof power of information leaks into an adjacent frequency. Therefore,performing the distortion correction as explained in this embodiment hasa great effect.

For example, in a communication system where a signal band is broadwhile a plurality of channels is adjacent, it is necessary to selectonly a desired frequency signal component to extract. Achieving thisprocessing by a filter comprised of analog elements is extremelydifficult in terms of scale and accuracy.

Accordingly, in the convention system, a method is adopted where afilter for selecting a channel is comprised of a digital device.However, the filter comprised of a digital device needs to handle alsounnecessary frequency signal components until an analog signal isconverted into a digital signal. The problem thereby arises that interms of the frequency and dynamic range of the amplitude, the linearityshould be reserved by the analog element.

According to this embodiment, it is made possible to remove a distortionreadily from a received signal by inputting in advance the distortioncharacteristics of quantizing section 602 and the whole receivingconfiguration to distortion estimating section 602, whereby it ispossible to expand a range of the amplitude of manageable signals, andto make the reception apparatus miniaturized and inexpensive.

When a signal with large power transmitted on an adjacent channel isinput as an interfering signal to the digital reception apparatusaccording to this embodiment, it is necessary to set a range ofquantization in quantizing section 602 to be large. However, under thecondition that the resolution is the same in the quantization, thequantization errors are increased, and the characteristic of ademodulated signal deteriorates. Then, it is made possible to performnon-linear quantization in quantizing section 602, and to perform thedistortion correction corresponding to the non-linear quantization indistortion correcting section 603. It is thereby possible to provide aweight of the quantization error from a signal with low power to asignal with high power, and therefore even under the condition of thesame quantization resolution, the characteristic of a demodulated signaldoes not deteriorate in particular.

In the conventional method, the design on the linearity of elementscomposing the reception apparatus limits a range of received signals.Accordingly, the linearity of these elements is only maintained whencharacteristics of a received signal are predicted in advance. Accordingto this embodiment, since the linearity can be maintained in asufficiently wide range, the reception apparatus is effectiveparticularly in a demodulation system that does not limit receivedsignals in particular (for example, a system with the demodulatingsection achieved by software).

In the general reception apparatus, since the linearmodulation/demodulation is basically adopted, a linear amplifyingelement is used as receiving section 101. However, all the amplifyingelements have the distortion characteristic that the resultant isnon-linear with respect to an input signal. The distortioncharacteristic is often caused by that output signals are saturated, andusually remains constant with respect to the instantaneous power of aninput signal. Therefore, an input signal is uniquely determined withrespect to the output signal. Accordingly, only using an output signalof receiving section 101 (i.e., the received signal 150), distortioncorrecting section 603 is able to estimate an ideal output signal, inother words, to remove the distortion from the received signal 150 fromreceiving section 101.

Meanwhile, when an input signal is not uniquely determined with respectto the output signal(received signal 150) of receiving section 101,distortion correcting section 603 outputs the information on somecharacteristic (for example, power) of the received signal 150 todistortion correcting section 630, whereby it is made possible to removethe distortion from the received signal 150. Further, in this case, ifthe effect is limited, it is possible to estimate an ideal output signalfrom the output signal (received signal 150) of receiving section 101.However, in this case, there is a possibility that as a signal fromwhich the distortion is removed, such a signal is obtained that isdifferent from the ideal output signal.

When the distortion characteristic of quantizing section 602 is designedin advance, for example, when the distortion characteristic is designedby an arithmetical calculation, distortion correcting section 603 isreadily configured only with the inverse characteristic of thedistortion characteristic given thereto, which facilitates theconfiguration of distortion correcting section 603. Further, if it ispossible to measure or design in advance the distortion characteristicof quantizing section 602, it is possible to configure distortioncorrecting section 603 optimal for removing the distortioncharacteristic, and furthermore, for example, by representing a changein the distortion characteristic of quantizing section 602 by anarithmetical calculation or storing the change in a reference table, itis possible to configure distortion correcting section 603 with highapplicability.

While this embodiment limits a distortion that distortion correctingsection 603 corrects to only a distortion generated in quantizingsection 602, the distortion that distortion correcting section 603corrects is not limited in particular. Distortion correcting section 603may perform overall corrections including distortions generated inelements such as receiving section 101 besides the distortion caused byquantizing section 602, whereby it is obvious that the distortioncorrection effects with high accuracy can be obtained.

Distortion correcting section 303 handles quantization information, andtherefore is capable of being composed of a conventional logicalcircuit, or of being achieved by the software (computer program).

Seventh Embodiment

FIG. 7 is a block diagram illustrating a configuration of a digitalreception apparatus according to the seventh embodiment of the presentinvention. In addition, in FIG. 7, the same sections as in the fifthembodiment (FIG. 5) are assigned the same reference numerals as in FIG.5, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, gain adjusting section 701, amplifyingsection 102, quadrature demodulation section 201, quantizing section401, distortion correcting section 703 having distortion estimatingsection 704 a and distortion compensating sections 202 b and 202 c,filtering section 501, and control section 702.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only given to points differentfrom the fifth embodiment.

The received signal 150 from receiving section 101 is subjected toamplitude adjustment in gain adjusting section 701. Gain adjustingsection 701 thereby outputs a gain adjusted signal 750 to amplifyingsection 102. In addition, gain adjusting section 701 performs theamplitude adjustment based on a gain control signal 751 from controlsection 702. The gain control signal 751 will be described specificallylater.

The gain adjusted signal 750 is amplified in amplifying section 102, andthen output to quadrature demodulation section 201. The processingperformed in from quadrature demodulation section 201 to filteringsection 501 is the same as in the fifth embodiment, and the detailedexplanations are omitted. The in-phase signal 550 b and quadraturesignal 550 c in the band limited baseband signal obtained in filteringsection 501 are output to control section 702.

Signal components necessary for the demodulation are only input tocontrol section 702 from among the in-phase signal 250 b and quadraturesignal 250 c in the baseband signal obtained in quadrature demodulationsection 201. In other words, the in-phase signal 550 b and quadraturesignal 550 c in the band limited baseband signal correspond to thesignal components necessary for the demodulation (specifically, thesignal obtained by removing from a received signal a signalcorresponding to a channel used by another communication apparatus otherthan the digital reception apparatus). The aforementioned signalcomponents necessary for the demodulation are equal to signal componentscorresponding to a desired signal contained in the received signal.

Accordingly, if the amplitude is controlled in gain adjusting section701 based on the amplitude of in-phase signal 550 b and quadraturesignal 550 c in the band limited baseband signal obtained in filteringsection 501, it is possible to expand a dynamic range of each of thein-phase signal 550 b and quadrature signal 550 c in the band limitedbaseband signal. That is, it is possible to perform the gain control onthe amplitude of a desired signal. It is thereby possible to prevent thereception characteristic from deteriorating.

Specifically, in order to bring the amplitude of the in-phase signal 550b and quadrature signal 550 c in the band limited baseband signal closeto a predetermined required value, control section 702 generates asuppressing signal for suppressing the gain in gain adjusting section701 when the amplitude of the in-phase signal 550 b and quadraturesignal 550 c is more than the required value, while generating anincreasing signal for increasing the gain in gain adjusting section 701when the amplitude of the in-phase signal 550 b and quadrature signal550 c is less than the required value. The thus generated suppressingsignal or increasing signal is output to gain adjusting section 701 asthe gain control signal 751.

Meanwhile, in the conventional system, when an interfering signal withan excessive level is received, a method is adopted that suppresses thewhole level of the received signal so as not to generate a distortion inthe receiving configuration. In this method, with the received signallevel suppressed, the amplitude of the desired signal contained in thereceived signal is also suppressed, and therefore the receptioncharacteristic deteriorates.

Control section 702 outputs the gain control signal 751 also todistortion estimating section 704 a in distortion correcting section703. Distortion estimating section 704 a also refers to the gain controlsignal 751 when the section 704 a estimates distortions contained in thein-phase signal 450 b and quadrature signal 450 c in the quantizedbaseband signal.

In addition, it is naturally possible for control section 702 to performthe gain control with higher accuracy by monitoring the amplitude of aninterfering signal and received signal, as well as the desired signal.Control section 702 further performs the gain control including theamplitude of signals necessary for the demodulation in the demodulatingsection, whereby it is possible to, for example, monitor an effect dueto a distortion. It is thereby possible to perform the gain control withhigher accuracy.

Since amplifying section 102 has the distortion characteristic thatremains constant with respect to the amplitude of an input signal (oroutput signal), gain adjusting section 701 that controls the amplitudeof the gain adjusted signal 750 to be input to amplifying section 102 isable to control the distortion characteristic of amplifying section 102.Components of the distortion characteristic of amplifying section 102represented by vectors are not lost after being subjected to thequadrature demodulation in quadrature demodulation section 201. Byinputting in advance the characteristic of amplifying section 102 todistortion estimating section 704 a, distortion estimating section 704 ais able to estimate the distortion components caused by amplifyingsection 102, and distortion compensating sections 202 b and 202 c areable to remove the distortion components caused by amplifying section102. According to such a method, since the distortion characteristic isrepresented by vectors, the distortion correcting section is able tocorrect the amplitude distortion and phase distortion. It is therebypossible to reserve the particularly high linearity.

Further, the received signals are processed as digital signals when thedistortion correction is performed thereto. The digital receptionapparatus according to this embodiment is thereby capable of obtainingthe characteristics with high accuracy and with stability.

According to this embodiment, it is possible to use even an amplifyingelement having a distortion in a demodulating system requiring thelinearity. In particular, under the condition that a distortion isgenerated in an analog element, it is impossible to expect the effectsas designed to an element such as a filter for performing processing ona frequency axis. Accordingly, even using the filter, it is sometimesimpossible to prevent the occurrence of an adverse effect such that partof power of information leaks into an adjacent frequency. Therefore,performing the distortion correction as explained in this embodiment hasa great effect.

For example, in a communication system where a signal band is broadwhile a plurality of channels is adjacent, it is necessary to selectonly a desired frequency signal component to extract. Achieving thisprocessing by a filter comprised of analog elements is extremelydifficult in terms of scale and accuracy.

Accordingly, in the convention system, a method is adopted where afilter for selecting a channel is comprised of a digital device.However, the filter comprised of a digital device needs to handle alsounnecessary frequency signal components until an analog signal isconverted into a digital signal. The problem thereby arises that interms of the frequency and dynamic range of the amplitude, the linearityshould be reserved by the analog element.

According to this embodiment, it is made possible to remove a distortionreadily from a received signal by inputting in advance the distortioncharacteristics of the whole receiving configuration to distortionestimating section 704 a, whereby it is possible to expand a range ofthe amplitude of manageable signals, and to make the reception apparatusminiaturized and inexpensive.

When a signal with large power transmitted on an adjacent channel isinput as an interfering signal to the digital reception apparatusaccording to this embodiment, it is necessary to set a range ofquantization in quantizing section 401 to be large. However, under thecondition that the resolution is the same in the quantization, thequantization errors are increased, and the characteristic of ademodulated signal deteriorates. Then, it is possible to provide adistortion characteristic for limiting the amplitude to the amplifiedsignal in the amplifying section disposed at a first half, and toperform the distortion correction corresponding to the distortioncharacteristic in distortion correcting section at a latter half. It isthereby possible to provide a weight of the quantization error from asignal with low power to a signal with high power, and therefore evenunder the condition of the same quantization resolution, thecharacteristic of a demodulated signal does not deteriorate inparticular.

In the conventional method, the design on the linearity of elementscomposing the reception apparatus limits a range of received signals.Accordingly, the linearity of these elements is only maintained whencharacteristics of a received signal are predicted in advance. Accordingto this embodiment, since the linearity can be maintained in asufficiently wide range, the reception apparatus is effectiveparticularly in a demodulation system that does not limit receivedsignals in particular (for example, a system with the demodulatingsection achieved by software).

In the general reception apparatus, since the linearmodulation/demodulation is basically adopted, a linear amplifyingelement is used as amplifying section 102. However, all the amplifyingelements have the distortion characteristic that the resultant isnon-linear with respect to an input signal. The distortioncharacteristic is often caused by that output signals are saturated, andusually remains constant with respect to the instantaneous power of aninput signal. Therefore, an input signal is uniquely determined withrespect to the output signal. Accordingly, only using an output signalof amplifying section 102 (i.e., the amplified signal 151), distortioncorrecting section 703 is able to estimate an ideal output signal, inother words, to remove the distortion from the amplified signal 151 fromamplifying section 102.

Meanwhile, when an input signal (gain adjusted signal 750) is notuniquely determined with respect to the output signal (amplified signal151) of amplifying section 102, distortion correcting section 703outputs the information on some characteristic (for example, power) ofthe gain adjusted signal 750 to distortion correcting section 730without passing the information through amplifying section 102, wherebyit is made possible to remove the distortion from the received signal150. Further, in this case, if the effect is limited, it is possible toestimate an ideal output signal from the output signal (amplified signal151) of amplifying section 102. However, in this case, there is apossibility that as a signal from which the distortion is removed, sucha signal is obtained that is different from the ideal output signal.

When the distortion characteristic of amplifying section 102 is designedin advance, for example, when the distortion characteristic is designedby an arithmetical calculation, distortion correcting section 703 isreadily configured only with the inverse characteristic of thedistortion characteristic given thereto, which facilitates theconfiguration of distortion correcting section 703. Further, if it ispossible to measure or design in advance the distortion characteristicof amplifying section 102, it is possible to configure distortioncorrecting section 703 optimal for removing the distortioncharacteristic, and furthermore, for example, by representing a changein the distortion characteristic of amplifying section 102 by anarithmetical calculation or storing the change in a reference table, itis possible to configure distortion correcting section 703 with highapplicability.

While this embodiment limits a distortion that distortion correctingsection 703 corrects to only a distortion generated in amplifyingsection 102, the distortion that distortion correcting section 703corrects is not limited in particular. Distortion correcting section 703may perform overall corrections including distortions generated inelements such as receiving section 101 besides the distortion caused byamplifying section 102, whereby it is obvious that the distortioncorrection effects with high accuracy can be obtained.

While in this embodiment, amplifying section 102 and quantizing section401 are provided as independent elements, it may be possible toalternate the position of amplifying section 102 and that of quadraturedemodulation section 201 to provide amplifying section 102 as an inputamplifier for quantizing section 401. In this case, a non-linearquantizing element may be composed of amplifying section 102 andquantizing section 401.

Eighth Embodiment

FIG. 8 is a block diagram illustrating a configuration of a digitalreception apparatus according to the eighth embodiment of the presentinvention. In addition, in FIG. 8, the same sections as in the sixthembodiment (FIG. 6) are assigned the same reference numerals as in FIG.6, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, gain adjusting section 801, filteringsection 301, quadrature demodulation section 601, quantizing section602, distortion correcting section 802, filtering section 604, andcontrol section 803.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only given to points differentfrom the sixth embodiment.

The received signal 150 from receiving section 101 is subjected toamplitude adjustment in gain adjusting section 801. Gain adjustingsection 801 thereby outputs a gain adjusted signal 850 to filteringsection 301. In addition, gain adjusting section 801 performs theamplitude adjustment based on a gain control signal 851 from controlsection 803. The gain control signal 851 will be described specificallylater.

The gain adjusted signal 850 is subjected to band limitation infiltering section 301, and then output to quadrature demodulationsection 201. The processing performed in from quadrature demodulationsection 601 to filtering section 604 is the same as in the sixthembodiment, and the detailed explanations are omitted. An in-phasesignal 653 b and quadrature signal 653 c in the band limited basebandsignal obtained in filtering section 604 are output to control section803.

Signal components necessary for the demodulation are only input tocontrol section 803 from among the in-phase signal 650 a and quadraturesignal 650 b in the baseband signal obtained in quadrature demodulationsection 601. In other words, the in-phase signal 653 a and quadraturesignal 653 b in the band limited baseband signal correspond to thesignal components necessary for the demodulation (specifically, thesignal obtained by removing from a received signal a signalcorresponding to a channel used by another communication apparatus otherthan the digital reception apparatus).

Accordingly, if the amplitude is controlled in gain adjusting section801 based on the amplitude of the in-phase signal 653 a and quadraturesignal 653 b in the band limited baseband signal obtained in filteringsection 604, it is possible to expand a dynamic range of each of thein-phase signal 653 a and quadrature signal 653 b in the band limitedbaseband signal. That is, it is possible to perform the gain adjustmenton the amplitude of a desired signal. It is thereby possible to preventthe reception characteristic from deteriorating.

Specifically, in order to bring the amplitude of in-phase signal 653 aand quadrature signal 653 b in the band limited baseband signal close toa predetermined required value, control section 803 generates asuppressing signal for suppressing the gain in gain adjusting section801 when the amplitude of the in-phase signal 653 a and quadraturesignal 653 b is more than the required value, while generating anincreasing signal for increasing the gain in gain adjusting section 801when the amplitude of the in-phase signal 653 a and quadrature signal653 b is less than the required value. The thus generated suppressingsignal or increasing signal is output to gain adjusting section 801 asthe gain control signal 851.

Meanwhile, in the conventional system, when an interfering signal withan excessive level is received, a method is adopted that suppresses thewhole level of the received signal so as not to generate a distortion inthe receiving configuration. In this method, with the received signallevel suppressed, the amplitude of the desired signal contained in thereceived signal is also suppressed, and therefore the receptioncharacteristic deteriorates.

Control section 803 outputs the gain control signal 851 also todistortion correcting section 802. Distortion correcting section 802also refers to the gain control signal 851 when the section 802linearizes the in-phase signal 650 a and quadrature signal 650 b in thenon-linear quantized signal.

In addition, it is naturally possible for control section 803 to performthe gain control with higher accuracy by monitoring the amplitude of aninterfering signal and received signal, as well as the desired signal.Control section 803 further performs the gain control including theamplitude of signals necessary for the demodulation in the demodulatingsection, whereby it is possible to, for example, monitor an effect dueto a distortion. It is thereby possible to perform the gain control withhigher accuracy.

Quantizing section 602 has the distortion characteristic that remainsconstant with respect to the amplitude of an input signal (or outputsignal). By inputting in advance the distortion characteristic todistortion correcting section 802, using the distortion characteristic,distortion correcting section 802 is able to linearize the non-linearquantized signal obtained in quantizing section 602. Further, thenon-linear quantized signal is processed as a digital signal when thedistortion correction is performed thereto. The digital receptionapparatus according to this embodiment is thereby capable of obtainingthe characteristics with high accuracy and with stability.

In the conventional quantization, the whole range of the amplitudeavailable for received signals to be quantized is divided into aplurality of quantization steps each with a constant signal width, andeach quantization step is assigned a code specific to the quantizationstep. This processing equals dispersing a quantization error over allthe signals with equal levels. Then, the whole range of the amplitudeavailable for received signals to be quantized is divided into aplurality of quantization steps with mutually different signal widths,and each quantization step is subjected to demodulation specific to thequantization step, whereby the quantization error changes, and thereforecan be adjusted corresponding to the amplitude of the signal.

Using the above processing enables the adjustment of a noise to beprovided to the digital reception apparatus. The receptioncharacteristics of the digital reception apparatus are determined by asystem noise represented by noise index, quantization error, calculationerror, etc. The system noise remains almost constant regardless ofreceived level, and the effect of the calculation error tends todecrease as the amplitude of a signal to be processed increases.

Therefore, for example, by making the sum of the quantization error andcalculation error constant, or by sacrificing the characteristic at ahigh C/N environment, it is possible to increase the quantization erroras the amplitude of a signal increases. Specifically, the quantizingsection assigns a quantization step with a small signal width to areceived signal with the small amplitude, while assigning a quantizationstep with a large signal width to a received signal with the largeamplitude. The quantization noise caused by the quantization error isthereby weighted largely on the received signal with the largeamplitude, whereby it is possible to make the sum of the quantizationerror and calculation error constant.

Using such non-linear quantization, it is possible to expand the wholerange of the amplitude of received signals to be quantized withoutincreasing the quantization number (resolution). Further, by adjustingquantization steps to be optimal, it is possible to achieve thequantization with the small quantization number. In particular, bydesigning the quantization steps corresponding to a modulation schemeused in communications and an expected reception environment, it ispossible to design a digital reception apparatus that performs highlyefficient reception.

Distortion correcting section 802 performs the processing using thevector calculation, whereby it is possible to correct the amplitudedistortion and phase distortion generated in receiving section 101.

According to this embodiment, it is possible to use even an amplifyingelement having a distortion in a demodulating system requiring thelinearity. In particular, under the condition that a distortion isgenerated in an analog element, it is impossible to expect the effectsas designed to an element such as a filter for performing processing ona frequency axis. Accordingly, even using the filter, it is sometimesimpossible to prevent the occurrence of an adverse effect such that partof power of information leaks into an adjacent frequency. Therefore,performing the distortion correction as explained in this embodiment hasa great effect.

For example, in a communication system where a signal band is broadwhile a plurality of channels is adjacent, it is necessary to selectonly a desired frequency signal component to extract. Achieving thisprocessing by a filter comprised of analog elements is extremelydifficult in terms of scale and accuracy.

Accordingly, in the convention system, a method is adopted where afilter for selecting a channel is comprised of a digital device.However, the filter comprised of a digital device needs to handle alsounnecessary frequency signal components until an analog signal isconverted into a digital signal. The problem thereby arises that interms of the frequency and dynamic range of the amplitude, the linearityshould be reserved by the analog element.

According to this embodiment, it is made possible to remove a distortionreadily from a received signal by inputting in advance the distortioncharacteristics of quantizing section 602 and the whole receivingconfiguration to distortion correcting section 802, whereby it ispossible to make the reception apparatus miniaturized and inexpensive.

When a signal with large power transmitted on an adjacent channel isinput as an interfering signal to the digital reception apparatusaccording to this embodiment, it is necessary to set a range ofquantization in quantizing section 602 to be large. However, under thecondition that the resolution is the same in the quantization, thequantization errors are increased, and the characteristic of ademodulated signal deteriorates. Then, it is made possible to performnon-linear quantization in quantizing section 602, and to perform thedistortion correction corresponding to the non-linear quantization indistortion correcting section 802. It is thereby possible to provide aweight of the quantization error from a signal with low power to asignal with high power, and therefore even under the condition of thesame quantization resolution, the characteristic of a demodulated signaldoes not deteriorate in particular.

In the conventional method, the design on the linearity of elementscomposing the reception apparatus limits a range of received signals.Accordingly, the linearity of these elements is only maintained whencharacteristics of a received signal are predicted in advance. Accordingto this embodiment, since the linearity can be maintained in asufficiently wide range, the reception apparatus is effectiveparticularly in a demodulation system that does not limit receivedsignals in particular (for example, a system with the demodulatingsection achieved by software).

In the general reception apparatus, since the linearmodulation/demodulation is basically adopted, linear amplifying elementsare used as receiving section 101 and gain adjusting section 801.However, all the amplifying elements have the distortion characteristicthat the resultant is non-linear with respect to an input signal. Thedistortion characteristic is often caused by that output signals aresaturated, and usually remains constant with respect to theinstantaneous power of an input signal. Therefore, an input signal isuniquely determined with respect to the output signal. Accordingly, onlyusing an output signal of receiving section 101 (i.e., the receivedsignal 150) and an output signal of gain adjusting section 801 (i.e.,gain adjusted signal 850), distortion correcting section 802 is able toestimate an ideal output signal, in other words, to remove thedistortion from the received signal 150 from receiving section 101.

Meanwhile, when respective input signal are not uniquely determined withrespect to the output signal (received signal 150) of receiving section101 and the output signal (gain adjusted signal 850) of gain adjustingsection 801, distortion correcting section 802 outputs the informationon some characteristics (for example, power) of the output signal ofreceiving section 101 (i.e., the received signal 150) and the outputsignal of gain adjusting section 801 (i.e., gain adjusted signal 850) todistortion correcting section 802, whereby it is made possible to removethe distortion. Further, in this case, if the effect is limited, it ispossible to estimate an ideal output signal from the output signal ofreceiving section 101 (the received signal 150) and the output signal ofgain adjusting section 801 (gain adjusted signal 850). However, in thiscase, there is a possibility that as a signal from which the distortionis removed, such a signal is obtained that is different from the idealoutput signal.

When the distortion characteristic of quantizing section 602 is designedin advance, for example, when the distortion characteristic is designedby an arithmetical calculation, distortion correcting section 802 isreadily configured only with the inverse characteristic of thedistortion characteristic given thereto, which facilitates theconfiguration of distortion correcting section 802. Further, if it ispossible to measure or design in advance the distortion characteristicof quantizing section 602, it is possible to configure distortioncorrecting section 802 optimal for removing the distortioncharacteristic, and furthermore, for example, by representing a changein the distortion characteristic of quantizing section 602 by anarithmetical calculation or storing the change in a reference table, itis possible to configure distortion correcting section 802 with highapplicability.

While this embodiment limits a distortion that distortion correctingsection 802 corrects to only a distortion generated in quantizingsection 602, the distortion that distortion correcting section 802corrects is not limited in particular. Distortion correcting section 802may perform overall corrections including distortions generated inelements such as receiving section 101 besides the distortion caused byquantizing section 602, whereby it is obvious that the distortioncorrection effects with high accuracy can be obtained.

Distortion correcting section 802 handles quantization information, andtherefore is capable of being composed of a conventional logicalcircuit, or of being achieved by the software (computer program).

Ninth Embodiment

FIG. 9 is a block diagram illustrating a configuration of a digitalreception apparatus according to the ninth embodiment of the presentinvention. In addition, in FIG. 9, the same sections as in the firstembodiment (FIG. 1) are assigned the same reference numerals as in FIG.1, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, non-linearly quantizing section 901,linearly compensating section 902, and demodulating section 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained.

The received signal from receiving section 101 is coded in non-linearlyquantizing section 901 to be a non-linear quantized coded signal 950. Atthis point, the quantization characteristics in non-linearly quantizingsection 901 are predetermined in accordance with the characteristics ofsignals to be quantized.

Herein, the details of the non-linear quantization performed bynon-linearly quantizing section 901 is explained with reference to FIGS.10A and 10B. FIG. 10A is a schematic view showing an example of therelationship between an input signal and output code in the conventionlinear quantization. FIG. 10B is a schematic view showing an example ofthe relationship between an input signal and output code in thenon-linear quantization in the digital reception apparatus according tothe ninth embodiment of the present invention.

A code c that is output by performing the linear quantization with aresolution N on a signal s is defined as indicated by the followingequation (1):c=Q(s,N)−(1)

FIG. 10A shown the relationship between the input signal s and thequantized code in performing the linear quantization according to theequation (1).

Specifically, the whole range of the amplitude (approximately −5 to +5in FIG. 10A) available for signals (received signals) to be quantized isdivided into a plurality of quantization steps each with a constantsignal width (the signal width A in FIG. 10A), and each quantizationstep is assigned an output code specific to the quantization step. Forexample, a quantization step 1001 with the signal width A is assigned anoutput code 7 specific to the quantization step 1001, while aquantization step 1002 with the signal A is assigned an output code −7specific to the quantization step 1002.

Meanwhile, the non-linear quantization is defined as performing thelinear-quantization on a non-linear signal s′ obtained by subjecting thesignal s to the non-linear processing f(x). A code c′ output by thenon-quantization is defined by the equation (2) shown below:c′=Q(s′,N)−(2)

Herein, it is assumed that the non-linear processing f( ) is determinedby the characteristics of signals to be quantized. As an example, thenon-linear processing f( ) is defined by the equation (3) shown below,using the appearance probability distribution p of the signal amplitude:S′=f(s,p)−(3)

Further, assuming the inverse function of the non-linear processing f( )is F( ) the following equation (4) is obtained:s=F(s′,p)−(4)

The non-linear processing function f( ) is a function such that s and s′are in unique relation to each other in the equations (3) and (4).

At this point, the linearity corresponds to satisfying the followingequation (5):s(x+y)=g(x)+g(y)−(5)

FIG. 10B shows the relationship between the input signal s and quantizedcode c′ when such non-linear quantization is performed.

Specifically, the whole range of the amplitude (approximately −5 to +5in FIG. 10B) available for signals (received signals) to be quantized isdivided into a plurality of quantization steps with mutually differentsignal widths, and each quantization step is assigned an output codespecific to the quantization step. For example, a quantization step 1003with a signal width B is assigned an output code 6 specific to thequantization step 1003, while a quantization step 1004 with a signalwidth C is assigned an output code −5 specific to the quantization step1004.

The width of each quantization step is determined based on theappearance probability of the amplitude of an input signal.Specifically, a quantization step corresponding to the amplitude withthe high probability of an input signal having the amplitude is assigneda smaller signal width, while a quantization step corresponding to theamplitude with the low probability of an input signal having theamplitude is assigned a larger signal width. For example, a quantizationstep (quantization step 1003) corresponding to an input signal with thelarger amplitude (for example, an input signal with the amplitude of 3)is assigned a larger signal width (signal width B), while a quantizationstep (quantization step 1005) corresponding to an input signal with thesmaller amplitude (for example, an input signal with the amplitude of0.5) is assigned a smaller signal width (signal width D(<B)).

Such non-linear quantization (FIG. 10B) is compared with theconventional linear quantization (FIG. 10A). Under the condition thatthe range of the signal width available for input signals is the same(in this case, approximately −5 to +5), codes of from approximately −13to +13 are needed as output codes when the linear quantization isapplied, while codes of from approximately −7 to +7 are needed as outputcodes when the non-linear quantization is applied.

In other words, applying the non-linear quantization suppresses theresolution required for coding the same input signal to be a lowerdegree than applying the linear quantization. There is a trade-offrelationship between the resolution and conversion rate in thequantization, and therefore suppressing the resolution enables theconversion rate in the quantization to be increased.

When a communication is applied which increases a signal amount percommunication band, the frequency of the received signal 150 fromreceiving section 101 in FIG. 9 is high, and therefore non-linearlyquantizing section 901 needs to perform the quantization faster. If theabove-mentioned non-linear quantization is applied in non-linearlyquantizing section 901, the section 901 is capable of suppressing theresolution, and therefore is capable of increasing the conversion ratein the quantization. Accordingly, the digital reception apparatusaccording to this embodiment is capable of coping with the case wherethe communication is applied which increases a signal amount percommunication band. The details of the non-linear quantization performedby non-linearly quantizing section 901 are as explained herein.

Referring to FIG. 9 again, a non-linear quantized code 950 obtained innon-linearly quantizing section 901 is output to linearly compensatingsection 902. Linearly compensating section 902 first generates a linearcompensated signal 951 that is the linear with respect to the non-linearquantized code 951, using the quantization characteristic (relationshipbetween the input signal and output code) in non-linearly quantizingsection 901.

At this point, the non-linear processing f( ) is predetermined, and theinverse function F( ) can be pre-calculated also. Accordingly,generating the linear compensated signal 951 using the non-linearquantized code 950 is readily achieved using a conversion table. Anexample of the conversion table is explained with reference to FIGS. 11Aand 11B. FIG. 11A is a schematic view illustrating an example of theconversion table (input signal versus non-linear quantized code) for useby non-linearly quantizing section 901 in the digital receptionapparatus according to the ninth embodiment of the present invention.FIG. 11B is a schematic view illustrating an example of the conversiontable (non-linear quantized code versus linearly compensated signal) foruse by linearly compensating section 902 in the digital receptionapparatus according to the ninth embodiment of the present invention.

When the received signal 150 is input to non-linearly quantizing section901, the section 901 outputs to linearly compensating section 902 anon-linear quantized code corresponding to the input signal (receivedsignal 150) in the conversion table, for example, shown in FIG. 11A. Inaddition, in the conventional method, a linear quantized code is outputwhich corresponds to the input signal in the conversion table, forexample, shown in the FIG. 11A.

After that, when the non-linear quantized code 950 is input to linearlycompensating section 902, linearly compensating section 902 outputs todemodulating section 104 linearization information corresponding to theinput code (non-linear quantized code 950) in the conversion table, forexample, shown in FIG. 11B. In addition, performing the non-linearquantization and linear compensation using the conversion tables shownin FIGS. 11A and 11B is explained only as an example. It may be possibleto achieve the non-linear quantization performed by non-linearlyquantizing section 901 and the linear compensation performed by linearlycompensating section 902 by respective calculation processing.

The linear compensated signal 951 obtained by linearly compensatingsection 902 is demodulated in demodulating section 104. A demodulatedsignal 952 is thereby obtained.

Generally, the processing performed by demodulating section 104 such asfiltering, synchronization and equalization is linear signal processingthat is executed on the assumption that the equation (5) is satisfied.In the linear quantized code that is subjected to the linearquantization, the linearity is maintained in the code itself.Accordingly, it is possible to subject the linear quantized code itselfas the linear information to the signal processing such as calculationprocessing. Meanwhile, the non-linear quantized code that is subjectedto the non-linear quantization does not satisfy the equation (5).Accordingly, it is not possible to subject the non-linear quantized codeto the conventional signal processing. However, with respect to thenon-linear quantized code subjected to the linearization describedabove, it is possible to perform the conventional demodulation in thesame way as in the linear quantized code.

The quantization error is next explained. A quantized error Eq is givenby the equation (6) shown below:

$\begin{matrix}{{Eq} = {\sum\limits_{k = {{- N}/2}}^{N/2}{\int_{{sk} - 1}^{sk}{\left( {{vk} - s} \right)^{2}{p(s)}{\mathbb{d}s}}}}} & (6)\end{matrix}$where N is the resolution, k is a quantized code, sk is a thresholdlevel between a code k and a code k+1, vk is a weight of a quantizedcode k, s is a signal to be quantized, and p(s) is the appearanceprobability of the signal s. As can be seen from the equation (6), thequantization error Eq varies with sk and vk, In the present invention,the adjustment of sk and the adjustment of vk in the equation (6) arerespectively performed by non-linearly quantizating section 901 andlinearly compensating section 902. As indicated by the equation (6),respective values of sk and vk are determined by the appearingprobability of a signal to be processed.

The effect of the quantization error provided by the equation (6) is notnegligible in recent communications where the multiplexing systembecomes complicated. Further, at the same time, with the communicationsignal band expanded, the demand has increased that requests to increasethe conversion rate in a quantizer. Furthermore, in order to decreaseeffects due to the quantization error, offset, etc., attraction is alsodrawn to IF sampling that is a scheme for quantizing IF signals.

Using such a scheme is capable of principally canceling errors caused bythe quadrature conversion. However, in the case of using the scheme,many subjects are concentrated on the quantizer. In other words, forexample, the quantizer is required a high conversion rate, and furtheris required a high resolution because even noises and interferingsignals which are not canceled in the IF band become signals to beprocessed by the quantizer.

In the present invention, using the non-linearly quantizing section andlinearly compensating section enables quantization steps to be arrangedoptimally. The quantization steps are set suitably for thecharacteristics of signals to be quantized, whereby it is possible tosuppress the occurrence of the quantization error to be fewer than thecase of using the conventional linear quantization. It is therebypossible to use a quantizer with a less resolution.

In addition, the explanation in this embodiment is given of the casewhere the quantization characteristic of non-linearly quantizing section901 is adapted to the characteristic of a signal to be quantized,however, the quantization characteristic may be determined by, as wellas the modulated signal to be received, communication systemenvironments and so on such as noises generated in a system, element,propagation path and the like, a modulated signal leaking from anotherchannel other than the communicating channel, and an expectedinterfering signal. Further, as characteristics of a signal to bequantized, there are considered a signal amplitude distribution,immunity of a modulated signal to a distortion, characteristics ofinterfering signals from adjacent and secondly adjacent channels and soon. Most of them vary with the communication condition. Accordingly, thecommunication condition is estimated by the demodulation, andcorresponding to the estimated result, the quantization characteristicis changed, whereby it is possible to reduce the power consumption.Specifically, for example, a quantization characteristic for suppressingthe interfering signal is used as the characteristic of a signal to bequantized in the case where the inference with the adjacent channel islarge, while the resolution on the quantization is decreased in the casewhere the received power is sufficiently high, whereby it is possible toreduce the power consumption.

Further, part of thresholds that are boundary values between quantizedcodes is made the same as the threshold used in the symbol decision of asignal to be processed, whereby it is possible to perform the symboldecision readily thereafter.

Furthermore, the case is explained where the non-linear distortion isgenerated by the operation of non-linearly quantizating section 901.However, as explained in each embodiment as described above, when adistortion is generated in an element in the receiving section, linearlycompensating section 902 needs to perform the compensation consideringthe distortion generated in the element besides the non-linearity ofnon-linearly quantizing section 901. Moreover, non-linearly quantizingsection 901 and linearly compensating section 902 may be composed of onedevice or one block.

As described previously, in the reception system using the IF sampling,it is difficult to design a filter that extracts only a desired signalfrom signals of IF band, and the IF signal itself has a higher frequencythan the baseband signal. Accordingly, in such a reception system, aload on the quantizing section is large. Also in this point, the presentinvention is effective particularly on the IF sampling system.

While the case is explained in this embodiment that a non-linearlyquantizing section is achieved by performing the non-linear processingprior to the linear quantization, a method for achieving thenon-linearly quantizing section is not limited to the above case. Forexample, the non-linearly quantizing section may be achieved by makingthresholds to be set for the quantization non-equal intervals, or if itis a type of Σ Δ, by changing the noise shaping method, filter design,or the like.

Further, while the case is explained that linearly compensating section902 is achieved by using the conversation table, any method is availableto compose linearly compensating section 902 as long as the section hasa function corresponding to the equation (4).

The digital reception apparatus according to this embodiment may becomposed of the software (computer program) in its partially or whollyconfiguration, and also in this case, the same effects as describedabove are obtained. The digital reception apparatus of this embodimentis capable of being used in a combination with any of the digitalreception apparatuses in the above-described embodiments.

Tenth Embodiment

FIG. 12 is a block diagram illustrating a configuration of a digitalreception apparatus according to the tenth embodiment of the presentinvention. In addition, in FIG. 12, the same sections as in the ninthembodiment (FIG. 9) are assigned the same reference numerals as in FIG.9, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, non-linearly quantizing section 901, linearcompensation calculating section 1201 having filter calculating section1202 and linearly compensating section 1203, filter coefficient storagesection 1204, and demodulating section 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only drawn to points differentfrom the ninth embodiment. The non-linear quantized code 950 obtained innon-linearly quantizing section 901 is output to filter calculatingsection 1202 in linear compensation calculating section 1201.

Filter coefficient storage section 1204 stores filter coefficients forthe filter calculation in filter calculating section 1202. Filtercoefficient storage section 1204 outputs a filter coefficient signal1250 indicative of the filter coefficients to filter calculating section1202.

Linear compensation calculating section 1201 is mainly composed offilter calculating section 1202 and linearly compensating section 1203.Filter calculating section 1202 receives its inputs the non-linearquantized code 950 and filter coefficient signal 1250. Filtercalculating section 1202 performs the filter calculation to thenon-linear quantized code 950 using the filter coefficient signal 1250.A calculated signal 1251 is obtained by the filter calculation. Theobtained calculated signal 1251 is linearized by linearly compensatingsection 1203, and then output to demodulating section 104 as a linearlycalculated signal 1252. Demodulating section 104 demodulates thelinearly calculated signal 1252, and thereby a demodulated signal 1253is obtained.

It is assumed herein that non-linearly quantizing section 901 performsthe quantization with a resolution of m bits, and that the filtercoefficient signal 1204 output from filter coefficient storage section1204 is a signal of n bits in its width.

As described previously, in the case of using the non-linearquantization, it is possible to achieve the quantization with the lessresolution than the case of using the conventional linear quantization.This is indicative of that the case of using the non-linear quantizationis capable of achieving the same reception performance as the case ofusing the conventional quantization with the less number of conditions(bits). If it is assumed that the resolution is decreased by x bits ascompared to the case of using the conventional linear quantization, inthe case of using the non-linear quantization, a signal having aninformation amount of m bits decreased by x bits is subjected to variouscalculations (for example, multiplication, division, addition,subtraction, etc.) in calculating circuits, and the thus calculatedsignal is subjected to the linear compensation processing, whereby it ispossible to make configurations of the calculating circuits simpler.

Further, with respect to the calculated signal 1251 output from filtercalculating section 1202, it may be possible to set a code length of thecalculated signal 1251 to an optimal code length, using the appearanceprobability distribution of the calculated signal 1251. Furthermore,with respect to the filter coefficient signal 1250 output from filtercoefficient storage section 1204, it may be possible similarly to set acode length of the filter coefficient signal 1250 to an optimal codelength. It is thereby possible to represent the non-linear quantizedcode 950 output from non-linearly quantizing section 901 by theresolution of further decreased n′ bits. Actually, the non-linearquantized code 950 and filter coefficient signal 1250 may be combinedoptimally to compose corresponding to conditions of communicationsignals, communication environments and so on, whereby it is possible toconfigure the calculating circuits further simply.

Thus, in this embodiment, a non-linearly quantized signal which is notlinearly compensated (for example, the non-linear quantized signal 950in FIG. 9) is subjected to various calculations by calculating circuits,instead of that a linearly compensated signal (for example, the linearcompensated signal 951 in FIG. 9) is subjected to various calculationsby calculating circuits. After that, the thus calculated signal issubjected to the linearizing compensation. It is thereby possible forcalculating circuits (such as an adder and multiplier) to performvarious calculations to a signal with the less number of conditions(bits), in other words, a signal with a small information amount. As aresult, it is possible to configure the calculating circuits remarkablysimply.

A fluctuation arises in the characteristic of a filter designed byanalog elements due to errors of the analog elements. Accordingly, in areceiver particularly for use in a digital communication, a channelfilter to select and extract only a desired received signal is oftencomposed of a digital filter. The technical idea indicated in thisembodiment has high compatibility with means for achieving theaforementioned digital filter. Further, it is possible to reduce thepower consumption by using the technical idea indicated in thisembodiment in a part requiring the operation with a high frequency suchas the IF sampling technique, the filtering processing used in imagecancellation performed after the digital quadrature demodulation, andthe like.

The case is explained in this embodiment that the filter coefficientsignal 1250 output from filter coefficient storage section 1204 is alinear signal. Further, it may be possible that filter coefficientstorage section 1204 outputs a linear signal as the filter coefficientsignal 1250, and that a converting section that converts a linear signalinto a non-linear signal is installed between filter coefficient storagesection 1204 and filter calculating section 1202. Thus, the linearsignal output from filter coefficient storage section 1204 is convertedinto the non-linear signal in the converting section and then output tofilter calculating section 1202.

Further, while the case is explained that each signal illustrated inFIG. 12 is represented by a constant code, each signal may be changedcorresponding to an actual reception environment or the like. In thiscase, it is possible to suppress effects due to unexpected deteriorationof environment characteristics and so on.

Furthermore, while the filter processing is explained as an example ofthe calculation processing, the same effects are obtained also in thecase where another processing (for example, various arithmeticcalculations) other than the filter processing is used as thecalculation processing. In particular, a larger effect is obtained inthe case where a multiplying circuit that increases the circuit scale isused as a circuit for performing the calculation processing.

While in this embodiment the case is explained that the logarithmconversion processing is used as the non-linear processing, it may bepossible to use another processing other than the logarithm conversionprocessing as the non-linear processing. Also in this case, the sameeffects as described above are obtained.

The digital reception apparatus according to this embodiment may becomposed of the software (computer program) in its partially or whollyconfiguration, and also in this case, the same effects as describedabove are obtained. The digital reception apparatus of this embodimentis capable of being used in a combination with any of the digitalreception apparatuses in the above-described embodiments.

Eleventh Embodiment

FIG. 13 is a block diagram illustrating a configuration of a digitalreception apparatus according to the eleventh embodiment of the presentinvention. In addition, in FIG. 13, the same sections as in the tenthembodiment (FIG. 12) are assigned the same reference numerals as in FIG.12, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, non-linearly quantizing section 901, linearcompensation calculating section 1302 having multiplying section 1301and linearly compensating section 1203, oscillating section 1303, anddemodulating section 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only drawn to points differentfrom the tenth embodiment. The non-linear quantized code 950 obtained innon-linearly quantizing section 901 is output to multiplying section1301 in linear compensation calculating section 1301.

Oscillating section 1303 outputs an oscillation signal 1352 composed ofa reference frequency for the frequency conversion to multiplyingsection 1301. Linear compensation calculating section 1302 is mainlycomposed of multiplying section 1301 and linearly compensating section1203.

Multiplying section 1301 receives its inputs the non-linear quantizedcode 950 and oscillation signal 1352. Multiplying section 1301multiplies the non-linear quantized code 950 by the oscillation signal1352. The multiplied result is linearized by linearly compensatingsection 1203, and then output to demodulating section 104 as a linearcalculated signal 1351. Demodulating section 104 demodulates the linearcalculated signal 1351, and thereby a demodulated signal 1353 isobtained.

It is herein assumed that as an example for simplifying the explanation,the non-linear processing given by the equation (3) described previouslyis a logarithmic variable given by the equation (7) shown below:s′=log(s)−(7)

Further, when it is assumed that the oscillation signal 1352 output fromoscillating section 1303 is also a logarithmic signal, the calculatedsignal 1350 output from multiplying section 1301 in FIG. 13 isrepresented by the equation (8) shown below:e′=log(s×lo)=log(s)+log(lo)=s′+lo′−(8)where e′ is the calculated signal 1350 represented by the logarithm, lois the oscillation signal 1352, and lo′ is the oscillation signal 1352represented by the logarithm.

The conversion table in linearly compensating section 1203 stores inadvance the conversion information that satisfies the equation (9) shownbelow:e=exp(e′)−(9)

It is obvious that the linear calculated signal 1351 (e in the equation(9)) is a signal having the linearity.

As described above, it is obvious that multiplying section 1301 can beconfigured by a multiplier, and thereby can be achieved with anextremely ready configuration.

While the explanation in this embodiment is given of the case using themultiplication calculation as an example of the calculation processing,most of the signal processing is composed of mainly addition,subtraction, multiplication and part of division. Then, a plurality ofcode systems is used so that the signal processing is divided into theaddition and subtraction, and multiplication and division, a calculatingsection for performing the addition and subtraction performs theprocessing with linear codes, and that another calculating section forperforming the multiplication and division performs the processing withlogarithmic codes, whereby the digital reception apparatus according tothis embodiment is capable of coping with a lot of signal processing.

As described previously, in the case of using the non-linearquantization, it is possible to achieve the quantization with the lessresolution than the case of using the conventional linear quantization.This is indicative of that the case of using the non-linear quantizationis capable of achieving the same reception performance as the case ofusing the conventional quantization with the less number of conditions(bits).

In this embodiment, a non-linearly quantized signal which is notlinearly compensated (for example, the non-linear quantized signal 950in FIG. 9) is subjected to various calculations by calculating circuits,instead of that a linearly compensated signal (for example, the linearcompensated signal 951 in FIG. 9) is subjected to various calculationsby calculating circuits. After that, the thus calculated signal issubjected to the linear compensation. It is thereby possible forcalculation circuits (such as an adder and multiplier) to performvarious calculations to a signal with a less number of conditions(bits), in other words, a signal with a small information amount. As aresult, it is possible to configure the calculation circuits remarkablysimply.

In particular, as described in the above embodiment, in a receiver usingthe IF sampling, a digital converted received is often subjected to thequadrature demodulation. Accordingly, the technical idea indicated inthis embodiment has high compatibility with the receiver using the IFsampling described above.

In this embodiment, the case is explained that the oscillation signal1352 output from oscillating section 1303 to multiplying section 1301 isa non-linear signal represented by the logarithm, however, it may bealso possible that the oscillation signal 1352 output from oscillatingsection 1303 is first input to a converting section to be subjected tothe logarithm conversion, and that the converted signal is input tomultiplying section 1301.

While the case is explained in this embodiment that the logarithmconversion is performed as the non-linear processing, the non-linearprocessing is not limited in particular. Also in other cases, the sameeffects as described above are obtained. Further, while the case isexplained that the multiplication is used as a calculation to beprocessed on the non-linear quantized code, the calculation to beprocessed on the non-linear quantized code is not limited to only themultiplication, and may include addition and other arithmeticcalculations.

The digital reception apparatus according to this embodiment may becomposed of the software (computer program) in its partially or whollyconfiguration, and also in this case, the same effects as describedabove are obtained. The digital reception apparatus of this embodimentis capable of being used in a combination with any of the digitalreception apparatuses in the above-described embodiments.

Twelfth Embodiment

FIG. 14 is a block diagram illustrating a configuration of a digitalreception apparatus according to the twelfth embodiment of the presentinvention. In addition, in FIG. 14, the same sections as in the tenthembodiment (FIG. 12) and in the eleventh embodiment (FIG. 13) areassigned the same reference numerals as in FIG. 12 and FIG. 13, and thedetailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, non-linearly quantizing section 901, linearcompensation calculating section 1401 having multiplying section 1301,filter calculating section 1202 and linearly compensating section 1203,filter coefficient storage section 1204, oscillating section 1303, anddemodulating section 104.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only drawn to points differentfrom the tenth and eleventh embodiments. The non-linear quantized code950 obtained in non-linearly quantizing section 901 is output tomultiplying section 1301 in linear compensation calculating section1401. Linear compensation calculating section 1401 is mainly composed ofmultiplying section 1301, filter calculating section 1202 and linearlycompensating section 1203.

Oscillating section 1303 outputs the oscillation signal 1352 composed ofa reference frequency for the frequency conversion to multiplyingsection 1301. Multiplying section 1301 receives its inputs thenon-linear quantized code 950 and oscillation signal 1352. Multiplyingsection 1301 multiplies the non-linear quantized code 950 by theoscillation signal 1352. The multiplied result is output to filtercalculating section 1202 as a multiplication calculated signal 1450.Filter calculating section 1202 has as input the filter coefficientsignal 1250 from filter coefficient storage section 1204.

Filter calculating section 1202 performs the filter calculation to themultiplication calculated signal 1450 using the filter coefficientsignal 1250. A filter calculated signal 1451 is obtained by the filtercalculation. The obtained filter calculated signal 1451 is linearized bylinearly compensating section 1203, and then output to demodulatingsection 104 as a linearly calculated signal 1452. Demodulating section104 demodulates the linearly calculated signal 1452, and thereby ademodulated signal 1453 is obtained.

It is herein assumed that as an example for simplifying the explanation,non-linear processing given by the equation (3) is a logarithmicvariable given by the equation (7).

Further, when it is assumed that the oscillation signal 1352 output fromoscillating section 1303 is also a logarithmic signal, themultiplication calculated signal 1450 obtained in multiplying section1301 in FIG. 14 is represented by the equation (8), where e′ is themultiplication calculated signal 1450 represented by the logarithm, lois the oscillation signal 1352, and lo′ is the oscillation signal 1352represented by the logarithm.

The code system of the multiplication calculated signal 1450 output frommultiplying section 1301 is set to be an optimal code system, using theappearance probability distribution of a signal to be decoded and thecalculation processing to be performed immediately thereafter (i.e., thefilter calculation by filter calculating section 1202). As an example,when the variance of the handled signal is large and the calculationprocessing to be performed immediately thereafter mainly includes themultiplication, the code system of the multiplication calculated signal1450 is set to codes based on the logarithm representation. Further whensuch calculation processing mainly includes the addition and requiresthe accuracy, the code system of the multiplication calculated signal1450 is set to linear codes.

The code system of the filter coefficient signal 1250 output from filtercoefficient storage section 1204 is assumed to the same code system asthe multiplication calculated signal 1450 described above. The codesystem is set to be optimal, using the appearance probabilitydistribution of the filter coefficient signal 1250 itself.

As described above, according to this embodiment, the optimal codesystems are provided corresponding to respective appearance probabilitydistributions of signals to be calculated and demodulated, whereby it ispossible to largely reduce the power consumption, circuit scale and soon. Further, with respect to a plurality of calculation processing, theoptimal code system is set for each input and output signal, whereby itis possible to suppress the scale of each calculation processing circuitto be a small scale. It is thereby possible to achieve theminiaturization and the reduced power consumption in the apparatus.

In this embodiment, the case is explained that multiplication and filterprocessing is used as the calculation processing, however, the sameeffects as described above are obtained also in the case where anotherprocessing is used as the calculation processing.

The digital reception apparatus according to this embodiment may becomposed of the software (computer program) in its partially or whollyconfiguration, and also in this case, the same effects as describedabove are obtained. The digital reception apparatus of this embodimentis capable of being used in a combination with any of the digitalreception apparatuses in the above-described embodiments.

Thirteenth Embodiment

FIG. 15 is a block diagram illustrating a configuration of a digitalreception apparatus according to the thirteenth embodiment of thepresent invention. In addition, in FIG. 15, the same sections as in thetwelfth embodiment (FIG. 14) are assigned the same reference numerals asin FIG. 14, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 101, non-linearly quantizing section 901, andnon-linearly demodulating section 1501 having filter calculating section1502, equalizer 1503, demodulating section 1504, and decision section1505.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only drawn to points differentfrom the twelfth embodiment. The non-linear quantized code 950 obtainedin non-linearly quantizing section 901 is converted into a signalrepresented by a code system optimal for the immediately-aftercalculation processing (i.e., the filter calculation in filtercalculating section 1502), and then output to filter calculating section1502 in non-linearly demodulating section 1502.

Filter calculating section 1502 performs the filter calculation usingthe non-linear quantized code 950 represented by the optimal codesystem, and predetermined filter coefficients. Further, the signalobtained by the filter calculation is converted into a signalrepresented by a code system optimal for the next calculation processing(i.e., equalizing processing in equalizer 1503). A filter signal 1551 isthereby obtained. The obtained filter signal 1551 is output to equalizer1503.

Equalizer 1503 performs the equalizing processing on the filter signal1551. Further, the signal obtained by the equalizing processing isconverted into a signal represented by a code system optimal for thedemodulation processing to be performed next (i.e., demodulationprocessing in demodulating section 1504). An equalized signal 1552 isthereby obtained. The obtained equalized signal 1552 is output todemodulating section 1504.

Demodulating section 1504 subjects the equalized signal 1552 to thedemodulation processing and various controls such as received powercontrol, frequency correction and synchronization processing. The signalobtained by the demodulation processing is converted into a signalrepresented by a code system optimal for the next calculation processing(i.e., decision processing in decision section 1505). A demodulatedsignal 1553 is thereby obtained. The obtained demodulated signal 1553 isoutput to decision section 1505.

Decision section 1505 performs symbol decision based on a thresholddetermined by an applied modulation scheme and the code system of thedemodulated signal 1553. The signal obtained by the symbol decision isoutput as a decided signal 1554.

While in this embodiment, the case is explained that the processingperformed by non-linearly demodulating section 1501 includes the filtercalculation, equalizing processing, demodulating processing and decisionprocessing, the processing performed by non-linearly demodulatingsection 1501 is not limited to the aforementioned calculation andprocessing, and may include all the general digital signal processing.

Further, while the case is explained that the hard decision is used suchthat decision section 1503 decides a symbol based on a threshold, it maybe possible for decision section 1505 to use the soft decision thatdecides a symbol sequence with the most likelihood based on a transitionof successive symbols.

In the method as the conventional technique where all the signalprocessing is processed with the same linear code, it is necessary touse the code system for coping with the case that the condition of areceived signal is the worst, and therefore there is a problem that thescale of the apparatus becomes large.

However, in this embodiment, circuits are designed so that the optimalcode system is set for each processing, and thereby it is possible toachieve the digital reception apparatus with a smaller circuit scale.

When the non-linear quantization is used where a width of eachquantization step is determined based on the appearance probability ofthe amplitude of an input signal, the dynamic range is expanded ascompared to the case of using the linear quantization, whereby stablecharacteristics are obtained even in receiving a signal with excessivepower that is not expected.

The modulated signal has the number of conditions corresponding to thenumber of modulation degrees (i.e., M in M-phase PSK or M-level QAM) ofthe applied modulation scheme. In the conventional demodulation scheme,the signal processing is performed on a signal with a condition the mostsimilar to that of an analog signal. Therefore, a large informationamount is necessary even in a proportion that does not need informationso much, providing problems that the circuit scale and power consumptionis increased.

Hence in this embodiment, the attention is drawn to the problems, and aninformation amount is optimized with respect to each calculationprocessing, whereby the miniaturization and reduced power consumption inthe whole apparatus can be achieved.

The digital reception apparatus according to this embodiment may becomposed of the software (computer program) in its partially or whollyconfiguration, and also in this case, the same effects as describedabove are obtained. The digital reception apparatus of this embodimentis capable of being used in a combination with any of the digitalreception apparatuses in the above-described embodiments.

Fourteenth Embodiment

FIG. 16 is a block diagram illustrating a configuration of a digitalreception apparatus according to the fourteenth embodiment of thepresent invention. In addition, in FIG. 16, the same sections as in thethirteenth embodiment (FIG. 15) are assigned the same reference numeralsas in FIG. 15, and the detailed explanations are omitted.

The digital reception apparatus according to this embodiment is providedwith receiving section 1601, non-linearly quantizing section 901, andnon-linearly demodulating section 1501 having filter calculating section1502, equalizer 1503, demodulating section 1604, and decision section1505, linearly compensating section 1602, and control section 1603.

The operation of the digital reception apparatus with the aboveconfiguration is explained with attention only drawn to points differentfrom the thirteenth embodiment.

Demodulating section 1504 performs the demodulation processing to theequalized signal 1552 as described previously. Further, from the signalobtained by the demodulation processing, various control information isextracted that includes information on the received power, informationon a frequency error, and information on a timewise synchronizationerror. The extracted various information is output as a controlinformation signal 1650 to linear compensating section 1602. Inaddition, the control information signal 1650 is a signal with nolinearity maintained, in other words, a non-linear signal.

The control information signal 1650 output from demodulating section1604 is subjected to linear compensation by linearly compensatingsection 1602, and then output to control section 1603 as a linearcontrol information signal 1651 with the linearity maintained.

Using the linear control information signal 1651, control section 1603generates a control signal 1652 including, for example, a gainadjustment control signal for instructing to adjust a gain in receivingsection 1601, a frequency control signal for instructing to adjust afrequency in receiving section 1601, and a timing control signal forinstructing to adjust a timing in a receiving section. The generatedcontrol signal 1652 is output to receiving section 1601. Receivingsection 1601 performs various controls based on the control signal 1652.

An analog section (specifically, receiving section 1601) is comprised ofvarious parts, and each part is designed to maintain the linearity withrespect to a control signal.

In this embodiment, by performing the signal processing using theinformation with the non-linearity, it is possible to achieve thesimplified circuit scale and reduced power consumption in a digitalsection (specifically, non-linearly demodulating section 1501). Further,the control signal output from the aforementioned digital section issubjected to the linear compensation, and thereby the linearity ismaintained in the signal. Accordingly, it is possible to use analogelements that have been used conventionally, as a part composing thereceiving section without modifying the elements. As a result, it is notnecessary to re-design the analog section described above newly.

In this embodiment, by using only linear codes as control signals outputfrom a digital section to an analog section, it is possible to readilyachieve the connection between the digital section using the non-linearcode and the analog section (controlled element) controlled by thedigital section.

While in this embodiment, the case is explained that all the controlsignals 1652 are of linear codes, it may be possible to use appropriateinformation for a portion for which a decibel representation isappropriate and generalized, instead of using the linear code as thecontrol signal 1652.

In the case where a controlled element has an error, for example,non-linear, with respect to a control signal, linearly compensatingsection 1602 may perform the linear compensation including such an errorcomponent, whereby it is possible to construct a control loop with lesserrors.

The digital reception apparatus according to this embodiment may becomposed of the software (computer program) in its partially or whollyconfiguration, and also in this case, the same effects as describedabove are obtained. The digital reception apparatus of this embodimentis capable of being used in a combination with any of the digitalreception apparatuses in the above-described embodiments.

The digital reception apparatus of each embodiment described above iscapable of being carried into practice in a combination thereof asappropriate.

As described above, the digital reception apparatus according to thepresent invention disperses a quantization noise appropriately, therebyreduces the effect due to the quantization error, and therefore enablesthe use of a quantizing section with a configuration simpler than theconventional method. Further, the digital reception apparatus accordingto the present invention is capable of using a receiving section with alarge distortion that has a difficulty in its use in the conventionalmethod, and therefore the present invention enables the miniaturization,cost reduction and improved performance of the apparatus.

The digital reception apparatus according to the present invention iscapable of replacing a receiving section with the high linearity,filtering section with the high performance, and quantizing section witha sufficient sampling rate and resolution, which have been required inparticular in a system of using a plurality of channels in a broadcommunication band, with respective sections with simpler andinexpensive configurations.

Further, the digital reception apparatus according to the presentinvention has the high adaptability to broad band signals and signalsapplied modulation schemes with a high signal density, and therefore itis possible to flexibly change the modulation scheme to be handled.

The digital reception apparatus according to the present invention asdescribed above is capable of being mounted on a communication terminalapparatus and base station apparatus in a digital mobile communicationsystem.

As obvious to those skilled in the art, the present invention is capableof being carried into practice by using a commercially available generaldigital computer and microprocessor with software programmed accordingto techniques as described in the above embodiments. Further as obviousto those skilled in the art, the present invention includes computerprograms made by those based on the techniques as described in the aboveembodiments.

The present invention includes computer program produces that arestorage media including the programs capable of being executed by acomputer for carrying out the present invention in practice. Thesestorage media include disks such as a floppy disk, optical disk, CD-ROMand magnetic disk, ROM, RAM, EPROM, EEPROM, optomagnetic card, memorycard and DVD, however, are not limited to the aforementioned materials.

The present invention is not limited to the above described embodiments,and various variations and modifications may be possible withoutdeparting from the scope of the present invention.

This application is based on the Japanese Patent ApplicationNo.2000-081226 filed on Mar. 23, 2000, entire content of which isexpressly incorporated by reference herein.

1. A digital reception apparatus, comprising: a receiver that performsreception processing on a received signal, the receiver comprising anon-linear quantizer that converts the received signal to a non-linearquantized signal; a distortion converter that converts the non-linearquantized signal to a linear signal for demodulation, the distortionconverter comprising a linear compensator, the non-linear quantizedsignal being input to the linear compensator which determines acorrecting signal that is indicative of an inverse characteristic of thenon-linear quantized signal, the correcting signal being utilized by thelinear compensator to convert the non-linear quantized signal to thelinear signal, the linear compensator further comprising: a filtercalculator that performs a filter calculation on the non-linearquantized signal.
 2. The digital reception apparatus according to claim1, wherein the linear compensator corrects the non-linear distortionusing at least a non-linear quantization characteristic of thequantizer.
 3. The digital reception apparatus according to claim 1,wherein the received signal comprises an instantaneous signal.
 4. Adigital reception apparatus, comprising: a receiver that performsreception processing on a received signal, the receiver comprising anon-linear quantizer that converts the received signal to a non-linearquantized signal; a distortion converter that converts the non-linearquantized signal to a linear signal for demodulation, the distortionconverter comprising a linear compensator, the non-linear quantizedsignal being input to the linear compensator which determines acorrecting signal that is indicative of an inverse characteristic of thenon-linear quantized signal, the correcting signal being utilized by thelinear compensator to convert the non-linear quantized signal to thelinear signal, wherein the linear compensator comprises a distortioncompensator that multiplies the received signal and the correctingsignal to remove the non-linear distortion from the received signal.